Roll back pure-Rust absl::Mutex interface as it's not TSAN compatible

PiperOrigin-RevId: 1007063165

absl/synchronization/mutex.h

diff --git a/absl/synchronization/mutex.h b/absl/synchronization/mutex.h
index 57b6d3c..0fbc9a5 100644
--- a/absl/synchronization/mutex.h
+++ b/absl/synchronization/mutex.h
@@ -160,8 +160,7 @@
 //
 // See also `MutexLock`, below, for scoped `Mutex` acquisition.
 
-class ABSL_LOCKABLE ABSL_ATTRIBUTE_WARN_UNUSED
-    Mutex {
+class ABSL_LOCKABLE ABSL_ATTRIBUTE_WARN_UNUSED Mutex {
  public:
   // Creates a `Mutex` that is not held by anyone. This constructor is
   // typically used for Mutexes allocated on the heap or the stack.