Only have one API for unfiltered output

At the end of this series, the use of unfiltered output will be very
restricted -- only places that definitely need it will use it.  To
this end, I thought it would be good to reduce the number of
_unfiltered APIs that are exposed.  This patch changes gdb so that
only printf_unfiltered exists.  (After this patch, the f* variants
still exist as well, but those will be removed later.)