Problem: globalReturn can't be used with sourceType:module, and right now in ESLint we will detect this combination and set globalReturn to false. Arguably, this behavior is undesirable because ESLint is silently fixing a problem rather than letting the user know that it happened.

We recently just implemented sourceType: commonjs, which effectively makes ecmaFeatures.globalReturn obsolete, so there are several options we could pursue going forward:

1. We could remove ecmaFeatures.globalReturn altogether. I think this is the cleanest solution now that we have sourceType: commonjs, however, we would probably want to throw an error if ecmaFeatures.globalReturn is specified to let people know that it has been removed.
2. We could keep ecmaFeatures.globalReturn but throw an error if it is used with sourceType: module. This error would bubble up to ESLint and to the user, allowing them to fix their configuration.

In either case, we could remove the logic from ESLint completely.

Thoughts?