Remove unused exception parameter from multifeed/tables/RankingConfigTable.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: palmje

Differential Revision: D55548526

fbshipit-source-id: 081fb326da758a111e7f1243c0539f828808611e

Author: r-barnes

multipy/runtime/test_deploy_lib.cpp

@@ -54,7 +54,7 @@ bool raise_and_catch_exception(bool except) {
       throw MyError("yep");
     }
     return false;
-  } catch (MyError& c) {
+  } catch (MyError&) {
     return true;
   }
 }