Replace MIPS TraceSimMsg calls with Comment calls.

runtime/vm/assembler_mips.h

Index: runtime/vm/assembler_mips.h
===================================================================
--- runtime/vm/assembler_mips.h	(revision 44977)
+++ runtime/vm/assembler_mips.h	(working copy)
@@ -325,10 +325,6 @@
 
   // Debugging and bringup support.
   void Stop(const char* message);
-
-  // TODO(zra): TraceSimMsg enables printing of helpful messages when
-  // --trace_sim is given. Eventually these calls will be changed to Comment.
-  void TraceSimMsg(const char* message);
   void Unimplemented(const char* message);
   void Untested(const char* message);
   void Unreachable(const char* message);