Replace broccoli-file-remover with broccoli-funnel.

* Uses more intelligent caching (avoids repeated globbing).
* Does not have issue with accidentally following symlinks and causing upstream file deletion.
* Generally better ;)

Closes #2247.
Closes #2262.
Yeah, me too.  Using glob didn't have very good performance either, as we were globbing on every rebuild, and this is pretty costly. Funnel keeps a small cache so the same filepath does not need to be evaluated again.