tsan: remove expected race leftover

[dvyukov]

Summary

Remove nmissed_expected variable.
It's a leftover from removed "expected race" feature and is never incremented.

compiler-rt/lib/tsan/rtl/tsan_rtl.h

 #if !SANITIZER_GO
   bool after_multithreaded_fork;
 #endif
 
   MetaMap metamap;
 
   Mutex report_mtx;
   int nreported;
-  int nmissed_expected;
   atomic_uint64_t last_symbolize_time_ns;
 
   void *background_thread;
   atomic_uint32_t stop_background_thread;
 
   ThreadRegistry thread_registry;
 
   Mutex racy_mtx;

compiler-rt/lib/tsan/rtl/tsan_rtl.cpp

 #else
 static const u32 kThreadQuarantineSize = 64;
 #endif
 
 Context::Context()
     : initialized(),
       report_mtx(MutexTypeReport),
       nreported(),
-      nmissed_expected(),
       thread_registry(CreateThreadContext, kMaxTid, kThreadQuarantineSize,
                       kMaxTidReuse),
       racy_mtx(MutexTypeRacy),
       racy_stacks(),
       racy_addresses(),
       fired_suppressions_mtx(MutexTypeFired),
       clock_alloc(LINKER_INITIALIZED, "clock allocator") {
   fired_suppressions.reserve(8);
if (ctx->nreported) {
     failed = true;
 #if !SANITIZER_GO
     Printf("ThreadSanitizer: reported %d warnings\n", ctx->nreported);
 #else
     Printf("Found %d data race(s)\n", ctx->nreported);
 #endif
   }
 
-  if (ctx->nmissed_expected) {
-    failed = true;
-    Printf("ThreadSanitizer: missed %d expected races\n",
-        ctx->nmissed_expected);
-  }
-
   if (common_flags()->print_suppressions)
     PrintMatchedSuppressions();
 
   failed = OnFinalize(failed);
 
   return failed ? common_flags()->exitcode : 0;
 }