writerfilter: Kill TokenToIdsMap's, and use switches instead.

This seems to save another nearly 300k; and I guess the compiler will optimize
it better than using the unordered_map.

Change-Id: I5df5cd2afe3f4bedad69e1e3477211842c40a90c
writerfilter: getDefineName() is unused, kill it.

Change-Id: I7d733a509f8256d0c2bfbb4bbd91ed6924452051