Replace FaceMap and FaceMapEntry
The NLSR source currently has two classes that exist only to provide a mapping between a Face URI string and a Face ID integer in NFD. There are two reasons this is unnecessary:
- The FIB could maintain a simple string -> integer map that provides the exact same functionality without class bloat, and
- This information is already available in the Adjacent objects that the Nlsr class maintains.
Then, it is totally unnecessary to have this mapping, and as far as I can tell only serves to confuse maintenance programmers.