include, libctf, binutils: drop labels

include, libctf, binutils: drop labels

These have never been implemented properly and don't work with the linker or
deduplicator: BTF has nothing like them, so the default assumption should be
that we drop them.  If we need something like them in future, we can add
them back (which we do not expect).

Quite a bit of label detritus is left in libctf after this: it's tied up
with later changes so will be removed as part of later commits.  (Because
the entire thing is disabled, the non-compilability of this intermediate
state is not a concern.)