noSpecials vs no_specials

We have both of these functions, both of them are used in the `glmmTMB` code base, they do different things (and were developed at different times). Ugh, this is almost as bad (or worse) than `tools::package[._]dependencies`, `tools::package(V|_v)ersion` ...

* understand/document what each is supposed to do
* merge/refactor?

Locate noSpecials and no_specials in the repository and inspect their callers, including the glmmTMB usage, to compare their behavior. Done means documenting what each function is intended to do and reaching a clear decision on whether to merge or refactor them.

Written by the indexing model from the issue text.