pw_sync: Clean up InterruptSpinLock migration

Removes the remaining references to SpinLock/spin_lock/SPIN_LOCK
now that all customers have been migrated.

Change-Id: I248c983798fa47aa07fee8acf37dd770f1513f5c
Requires: pigweed-internal:10780
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/37541
Commit-Queue: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
diff --git a/pw_sync/BUILD b/pw_sync/BUILD
index 7151178..b882e47 100644
--- a/pw_sync/BUILD
+++ b/pw_sync/BUILD
@@ -124,7 +124,6 @@
 pw_cc_library(
     name = "interrupt_spin_lock_facade",
     hdrs = [
-        "public/pw_sync/spin_lock.h",
         "public/pw_sync/interrupt_spin_lock.h",
     ],
     includes = ["public"],
diff --git a/pw_sync/BUILD.gn b/pw_sync/BUILD.gn
index 583f6ea..eeaf60e 100644
--- a/pw_sync/BUILD.gn
+++ b/pw_sync/BUILD.gn
@@ -58,18 +58,6 @@
   sources = [ "mutex.cc" ]
 }
 
-# TODO(ewout): Finish the migration and remove this logic.
-if (pw_sync_SPIN_LOCK_BACKEND != "") {
-  assert(pw_sync_INTERRUPT_SPIN_LOCK_BACKEND == "",
-         "You cannot define the backend for pw::sync::InterruptSpinLock twice!")
-  pw_sync_INTERRUPT_SPIN_LOCK_BACKEND = pw_sync_SPIN_LOCK_BACKEND
-}
-
-pw_source_set("spin_lock") {
-  public_deps = [ ":interrupt_spin_lock" ]
-  public = [ "public/pw_sync/spin_lock.h" ]
-}
-
 pw_facade("interrupt_spin_lock") {
   backend = pw_sync_INTERRUPT_SPIN_LOCK_BACKEND
   public_configs = [ ":public_include_path" ]
diff --git a/pw_sync/backend.gni b/pw_sync/backend.gni
index ba8e6b0..21091eb 100644
--- a/pw_sync/backend.gni
+++ b/pw_sync/backend.gni
@@ -25,9 +25,6 @@
   # Backend for the pw_sync module's interrupt spin lock.
   pw_sync_INTERRUPT_SPIN_LOCK_BACKEND = ""
 
-  # TODO(ewout): migrate all users to pw_sync_INTERRUPT_SPIN_LOCK_BACKEND.
-  pw_sync_SPIN_LOCK_BACKEND = ""
-
   # Whether the GN asserts should be silenced in ensuring that a compatible
   # backend for pw_chrono_SYSTEM_CLOCK_BACKEND is chosen.
   # Set to true to disable the asserts.
diff --git a/pw_sync/public/pw_sync/spin_lock.h b/pw_sync/public/pw_sync/spin_lock.h
deleted file mode 100644
index 415837d..0000000
--- a/pw_sync/public/pw_sync/spin_lock.h
+++ /dev/null
@@ -1,26 +0,0 @@
-// Copyright 2021 The Pigweed Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License"); you may not
-// use this file except in compliance with the License. You may obtain a copy of
-// the License at
-//
-//     https://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-// License for the specific language governing permissions and limitations under
-// the License.
-#pragma once
-
-#include "pw_sync/interrupt_spin_lock.h"
-
-#ifdef __cplusplus
-
-namespace pw::sync {
-
-using SpinLock = InterruptSpinLock;
-
-}  // namespace pw::sync
-
-#endif  // __cplusplus
diff --git a/pw_sync_baremetal/BUILD.gn b/pw_sync_baremetal/BUILD.gn
index fd99f4a..881e807 100644
--- a/pw_sync_baremetal/BUILD.gn
+++ b/pw_sync_baremetal/BUILD.gn
@@ -34,9 +34,6 @@
 # global interrupts, so this implementation does not support simultaneous
 # multi-threaded environments including IRQs, and is only meant to prevent
 # data corruption.
-pw_source_set("spin_lock") {
-  public_deps = [ ":interrupt_spin_lock" ]
-}
 pw_source_set("interrupt_spin_lock") {
   public_configs = [
     ":public_include_path",
diff --git a/pw_sync_embos/BUILD.gn b/pw_sync_embos/BUILD.gn
index fe19f24..8d9a0f4 100644
--- a/pw_sync_embos/BUILD.gn
+++ b/pw_sync_embos/BUILD.gn
@@ -113,9 +113,6 @@
 }
 
 # This target provides the backend for pw::sync::InterruptSpinLock.
-pw_source_set("spin_lock") {
-  public_deps = [ ":interrupt_spin_lock" ]
-}
 pw_source_set("interrupt_spin_lock") {
   public_configs = [
     ":public_include_path",
diff --git a/pw_sync_freertos/BUILD.gn b/pw_sync_freertos/BUILD.gn
index f539afc..20782e3 100644
--- a/pw_sync_freertos/BUILD.gn
+++ b/pw_sync_freertos/BUILD.gn
@@ -113,9 +113,6 @@
 }
 
 # This target provides the backend for pw::sync::InterruptSpinLock.
-pw_source_set("spin_lock") {
-  public_deps = [ ":interrupt_spin_lock" ]
-}
 pw_source_set("interrupt_spin_lock") {
   public_configs = [
     ":public_include_path",
diff --git a/pw_sync_stl/BUILD.gn b/pw_sync_stl/BUILD.gn
index 5ac5185..2e71713 100644
--- a/pw_sync_stl/BUILD.gn
+++ b/pw_sync_stl/BUILD.gn
@@ -102,9 +102,6 @@
 }
 
 # This target provides the backend for pw::sync::InterruptSpinLock.
-pw_source_set("spin_lock") {
-  public_deps = [ ":interrupt_spin_lock" ]
-}
 pw_source_set("interrupt_spin_lock") {
   public_configs = [
     ":public_include_path",
diff --git a/pw_sync_threadx/BUILD.gn b/pw_sync_threadx/BUILD.gn
index 046d8e0..41d5b32 100644
--- a/pw_sync_threadx/BUILD.gn
+++ b/pw_sync_threadx/BUILD.gn
@@ -124,9 +124,6 @@
 
 # This target provides the backend for pw::sync::InterruptSpinLock, note that
 # this implementation does NOT support ThreadX w/ SMP.
-pw_source_set("spin_lock") {
-  public_deps = [ ":interrupt_spin_lock" ]
-}
 pw_source_set("interrupt_spin_lock") {
   public_configs = [
     ":public_include_path",