Remove unused exception parameter from files inc facer/engine/utils/StatsD.cpp

Summary:
`-Wunused-exception-parameter` has identified an unused exception parameter. This diff removes it.

This:
```
try {
    ...
} catch (exception& e) {
    // no use of e
}
```
should instead be written as
```
} catch (exception&) {
```

If the code compiles, this is safe to land.

Reviewed By: dmm-fb

Differential Revision: D51977749

fbshipit-source-id: aab6f8bcb8a0d9273b7894b8e85615d4a31cac86

Author: r-barnes

faiss/IndexIDMap.cpp

@@ -266,7 +266,7 @@ void IndexIDMap2Template<IndexT>::reconstruct(
         typename IndexT::component_t* recons) const {
     try {
         this->index->reconstruct(rev_map.at(key), recons);
-    } catch (const std::out_of_range& e) {
+    } catch (const std::out_of_range&) {
         FAISS_THROW_FMT("key %" PRId64 " not found", key);
     }
 }