Fix or remove nestedFunctionDecl

[krame505]

I have no idea why this even exists (actually, I might have added it back when I was first working on closures, before I knew what I was doing), but it is totally useless right now since any analysis defined here would be incoherent.

If we want to let extensions define analyses differently on regular and nested functions, this should become non-forwarding, and the entire contents duplicated from functionDecl. However, I have yet to see a case where this would actually be useful, so the production should probably just be removed for now, and any uses in the ableC concrete syntax replaced by functionDecl.

Might be a good task for somebody new who wants to gain confidence in refactoring ableC?