Remove unused exception parameter from velox/functions/lib/SubscriptU…

…til.cpp (facebookincubator#8767)

Summary:
Pull Request resolved: facebookincubator#8767

`-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: D53780438

fbshipit-source-id: c414827341cea1227983ba80c373f15d8c0aaa7b

velox/functions/lib/SubscriptUtil.cpp

@@ -318,23 +318,23 @@ namespace {
 std::exception_ptr makeZeroSubscriptError() {
   try {
     VELOX_USER_FAIL("SQL array indices start at 1");
-  } catch (const std::exception& e) {
+  } catch (const std::exception&) {
     return std::current_exception();
   }
 }
 
 std::exception_ptr makeBadSubscriptError() {
   try {
     VELOX_USER_FAIL("Array subscript out of bounds.");
-  } catch (const std::exception& e) {
+  } catch (const std::exception&) {
     return std::current_exception();
   }
 }
 
 std::exception_ptr makeNegativeSubscriptError() {
   try {
     VELOX_USER_FAIL("Array subscript is negative.");
-  } catch (const std::exception& e) {
+  } catch (const std::exception&) {
     return std::current_exception();
   }
 }