Remove unused exception parameter from multifeed/tools/zdb_dumper/main.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: D58830970

fbshipit-source-id: 94d55ac80b8bd98f08cdb8c0acb2ecfa3dfb14a4

Author: r-barnes

multipy/runtime/test_deploy.cpp

@@ -283,7 +283,7 @@ TEST(TorchpyTest, TaggingRace) {
         try {
           I.fromIValue(t);
           success++;
-        } catch (const std::runtime_error& e) {
+        } catch (const std::runtime_error&) {
           failed++;
         }
       }