Running rdeps / allrdeps queries without fetching all external dependencies

### Description of the problem / feature request:

Aloha!

Our team is using `rdeps` / `allrdeps` to query reverse dependencies of targets. For example, this lets us know that for a given change to a local target, what is the set of reverse dependencies we should also build and test in order to validate that change.

We noticed that when running the query like this:

```
bazel query --universe_scope=//local_reverse_dependencies/... --order_output=no "allrdeps(//updated_local_target:name)"
```

-- this command will fetch all external dependencies of `//local_reverse_dependencies/...` -- for example, all `http_file` files, all `rules_jvm_external` artifacts, all `rules_docker` images, etc.

But since any changes to `//updated_local_target:name` would not affect external dependencies, we're not sure why they need to be fetched.

Our ask is simply: **Is there a way to execute this query without requiring all external dependencies of `//local_reverse_dependencies/...` to be fetched?**

Thank you for your help!

### What operating system are you running Bazel on?

macOS Catalina 10.15.4 (19E287)

### What's the output of `bazel info release`?

```
>_ bazel info release
release 3.0.0
```

### Have you found anything relevant by searching the web?

We haven't seen anything else related to this on GitHub issues or elsewhere.