Remove use of bfd_uint64_t and similar

Requiring C99 means that uses of bfd_uint64_t can be replaced with
uint64_t, and similarly for bfd_int64_t, BFD_HOST_U_64_BIT, and
BFD_HOST_64_BIT.  This patch does that, removes #ifdef BFD_HOST_*
and tidies a few places that print 64-bit values.