Remove unused exception parameter from cachelib/allocator/tests/TestB…

…ase-inl.h

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: vrishal

Differential Revision: D52957797

fbshipit-source-id: 482d1b631904ce4bc8d72849f92e42992f80bb4a

cachelib/allocator/tests/TestBase-inl.h

@@ -52,7 +52,7 @@ std::vector<uint32_t> AllocatorTest<AllocatorT>::getValidAllocSizes(
     // size is a valid allocation size. If not, try again.
     try {
       util::allocateAccessible(alloc, poolId, key, size);
-    } catch (const std::invalid_argument& e) {
+    } catch (const std::invalid_argument&) {
       continue;
     }
     sizes.push_back(size);