Remove extra semi colon from deprecated/libmccpp/ThreadSafeClientPool…

….h (#3479)

Summary:
Pull Request resolved: #3479

`-Wextra-semi` or `-Wextra-semi-stmt`

If the code compiles, this is safe to land.

Reviewed By: palmje

Differential Revision: D57632759

fbshipit-source-id: 48bc23e87b3f518182085124c4c8e68ddbb3ca8f

tests/test_common_ivf_empty_index.cpp

@@ -23,7 +23,7 @@ namespace {
 
 int d = 64;
 
-}; // namespace
+} // namespace
 
 std::vector<float> get_random_vectors(size_t n, int seed) {
     std::vector<float> x(n * d);