Remove extra semi colon from internal_repo_rocksdb/repo/monitoring/pe…

…rf_context_imp.h

Summary:
`-Wextra-semi` or `-Wextra-semi-stmt`

If the code compiles, this is safe to land.

Reviewed By: dmm-fb

Differential Revision: D51778007

fbshipit-source-id: 5d1b20a3acc4bcc7cd7c204f2f73a14fc8f81883

monitoring/perf_context_imp.h

@@ -74,7 +74,8 @@ extern thread_local PerfContext perf_context;
 #define PERF_COUNTER_ADD(metric, value)        \
   if (perf_level >= PerfLevel::kEnableCount) { \
     perf_context.metric += value;              \
-  }
+  } \
+  static_assert(true, "semicolon required")
 
 // Increase metric value
 #define PERF_COUNTER_BY_LEVEL_ADD(metric, value, level)               \