move hash_any to utils/hash/hashfn.c

I just noticed (once again) that we have hash_any() declared in
src/access/hash.h (the header file for the hash index AM) rather than
somewhere in utils/, for no good reason other than perhaps there was no
better place when it was introduced.  This means that some files that
seem to just need hash_any end up pointlessly #including the whole AM
world upon themselves.

Would anybody object too hard if I move hash_any() and friends to
src/backend/utils/hash/hashfn.c and the declarations to
src/include/utils/hashutils.h?


-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services