roll: pigweed, pw_toolchain: pw_kvs: Remove unnecessary Key alias and test

pw_kvs originally used std::string_view for keys. A downstream project
wanted to use pw_kvs in C++14, so implemented pw::kvs::Key, a custom
version of std::string_view in e64daf43. That team later migrated to a
newer C++ standard, and Pigweed dropped C++14 support, so the Key
implementation was converted to an alias.

The Key alias is unused outside pw_kvs, so remove it. Also remove code
that hints at C++14 support, since it is not supported in Pigweed.

This is potentially a BREAKING CHANGE! References to pw::kvs::Key must
be replaced with std::string_view.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/229976

https://pigweed.googlesource.com/pigweed/pigweed
pigweed, pw_toolchain Rolled-Commits: 5e9e39285969463..9b242113ab06e86
Roller-URL: https://ci.chromium.org/b/8739431030426514801
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I031aad199d18c8bab5b35bfbfdcde79e188f790f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/showcase/sense/+/230142
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/MODULE.bazel b/MODULE.bazel
index 7fdf5c2..826cf4e 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -48,8 +48,8 @@
     module_name = "pigweed",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-08-16.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8739432507085685425.
-    commit = "5e9e39285969463893c92043ff509958ec5eec40",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8739431030426514801.
+    commit = "9b242113ab06e86dff052bfa60b5e01fc6fd7f8a",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed",
 )
 
@@ -57,8 +57,8 @@
     module_name = "pw_toolchain",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-08-16.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8739432507085685425.
-    commit = "5e9e39285969463893c92043ff509958ec5eec40",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8739431030426514801.
+    commit = "9b242113ab06e86dff052bfa60b5e01fc6fd7f8a",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed",
     strip_prefix = "pw_toolchain_bazel",
 )