Remove `TYPE_NFIELDS`, changing all the call sites to use
`type::num_fields` directly. This is quite a big diff, but this was
mostly done using sed and coccinelle. A few call sites were done by
hand.
gdb/ChangeLog:
* gdbtypes.h (TYPE_NFIELDS): Remove. Change all cal sites to use
type::num_fields instead.
Change-Id: Ib73be4c36f9e770e0f729bac3b5257d7cb2f9591