third_party/freertos: remove non-common header

The initial pw_source_set for FreeRTOS was set up to ensure that
FreeRTOSConfig_template.h couldn't be accidentally used. It turns
out this file is not distributed by FreeRTOS. This change removes
it accordingly.

Change-Id: I91e85611e21544035a6705069dbd823df6095637
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/30860
Commit-Queue: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Alexei Frolov <frolv@google.com>
diff --git a/third_party/freertos/BUILD.gn b/third_party/freertos/BUILD.gn
index 416f7e6..9b30c06 100644
--- a/third_party/freertos/BUILD.gn
+++ b/third_party/freertos/BUILD.gn
@@ -62,9 +62,6 @@
     sources = [
       "$dir_pw_third_party_freertos/Source/croutine.c",
       "$dir_pw_third_party_freertos/Source/event_groups.c",
-
-      # Put here to ensure it cannot be included.
-      "$dir_pw_third_party_freertos/Source/include/FreeRTOSConfig_template.h",
       "$dir_pw_third_party_freertos/Source/list.c",
       "$dir_pw_third_party_freertos/Source/queue.c",
       "$dir_pw_third_party_freertos/Source/stream_buffer.c",