Add API to Semantic to remove unresolved references in bulk

[overlookmotel]

#5305 added ScopeTree::delete_root_unresolved_reference API to delete an unresolved reference.

@Dunqing said in #5305 (review):

Upon further reflection, I think we may also need to add a high-level API to remove unresolved_references. We usually may need to remove a whole expression or type_annotation, and we also need to figure out if the references are resolved or unresolved. It's painful to remove these 🙃

I agree with Dunqing that this API is needed. Opening this issue to discuss what it'd look like / how it'd work.