Revert r240137 (Fixed/added namespace ending comments using clang-tidy. NFC)

Apparently, the style needs to be agreed upon first.

llvm-svn: 240390
diff --git a/llvm/lib/Support/Mutex.cpp b/llvm/lib/Support/Mutex.cpp
index 42867c9..c8d3844 100644
--- a/llvm/lib/Support/Mutex.cpp
+++ b/llvm/lib/Support/Mutex.cpp
@@ -110,7 +110,7 @@
   return errorcode == 0;
 }
 
-} // namespace llvm
+}
 
 #elif defined(LLVM_ON_UNIX)
 #include "Unix/Mutex.inc"