Remove extra semi colon from faiss/Clustering.cpp

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

If the code compiles, this is safe to land.

Reviewed By: algoriddle

Differential Revision: D52969138

fbshipit-source-id: bdde568b9bc6f4cc650e131a471a41f6bc2f3f95

faiss/Clustering.cpp

@@ -250,7 +250,7 @@ int split_clusters(
     return nsplit;
 }
 
-}; // namespace
+} // namespace
 
 void Clustering::train_encoded(
         idx_t nx,
@@ -617,7 +617,7 @@ void copy_columns(idx_t n, idx_t d1, const float* src, idx_t d2, float* dest) {
     }
 }
 
-}; // namespace
+} // namespace
 
 void ProgressiveDimClustering::train(
         idx_t n,