libctf: de-macroize LCTF_TYPE_TO_INDEX / LCTF_INDEX_TO_TYPE

libctf: de-macroize LCTF_TYPE_TO_INDEX / LCTF_INDEX_TO_TYPE

Making these functions is unnecessary right now, but will become much
clearer shortly.

While we're at it, we can drop the third child argument to
LCTF_INDEX_TO_TYPE: it's only used for nontrivial purposes that aren't
literally the same as getting the result from the fp in one place,
in ctf_lookup_by_name_internal, and that place is easily fixed by just
looking in the right dictionary in the first place.