Remove unused exception parameter from deeplearning/projects/flashlig…

…ht/flashlight/fl/tensor/backend/af/mem/DefaultMemoryManager.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: D53780600

fbshipit-source-id: b5bc449f334424fe14b2922a5365978440a521c1

flashlight/fl/tensor/backend/af/mem/DefaultMemoryManager.cpp

@@ -188,7 +188,7 @@ void* DefaultMemoryManager::alloc(
       // Perform garbage collection if memory can not be allocated
       try {
         ptr = this->deviceInterface->nativeAlloc(allocBytes);
-      } catch (std::exception& ex) {
+      } catch (std::exception&) {
         // FIXME: assume that the exception is due to out of memory, and don't
         // continue propagating it
         // If out of memory, run garbage collect and try again