Delete the remaining ROM monitor targets

Delete the remaining ROM monitor targets

Ref: https://sourceware.org/ml/gdb/2015-07/msg00011.html

All of these targets use gdb/monitor.c, which has bit rotted
years ago (I'd guess around ~6), and nobody seems to
have noticed:

 | target         | source               |
 |----------------+----------------------|
 | target dbug    | gdb/dbug-rom.c       |
 | target picobug | gdb/microblaze-rom.c |
 | target dink32  | gdb/dink32-rom.c     |
 | target m32r    | gdb/m32r-rom.c       |
 | target mon2000 | gdb/m32r-rom.c       |
 | target ppcbug  | gdb/ppcbug-rom.c     |

This deletes them, along with finally removing monitor.c.

A manual update will be done separately.

gdb/ChangeLog:
2015-08-24  Pedro Alves  <palves@redhat.com>

	* NEWS: Mention removed support for the various ROM monitors.
	* Makefile.in (ALL_TARGET_OBS): Remove dbug-rom.o, dink32-rom.o,
	ppcbug-rom.o, m32r-rom.o, dsrec.o and monitor.o from gdb_target_obs.
	* configure.tgt (h8300-*-*): Remove monitor.o and m32r-rom.o from
	gdb_target_obs.
	(m68*-*-*): Remove monitor.o dbug-rom.o and dsrec.o from
	gdb_target_obs.
	(microblaze*-linux-*): Remove microblaze-rom.o, monitor.o and
	dsrec.o from gdb_target_obs.
	(microblaze*-*-*): Remove microblaze-rom.o, monitor.o and dsrec.o
	from gdb_target_obs.
	(powerpc-*-lynx*178): Remove monitor.o and dsrec.o from
	gdb_target_obs.
	(powerpc*-*-*): Remove monitor.o, dsrec.o, ppcbug-rom.o and
	dink32-rom.o from gdb_target_obs.
	(sh*-*-linux*): Remove monitor.o and dsrec.o from gdb_target_obs.
	(sh*): Remove monitor.o and dsrec.o from gdb_target_obs.
	* dbug-rom.c, dink32-rom.c, dsrec.c, m32r-rom.c, microblaze-rom.c,
	monitor.c, monitor.h, ppcbug-rom.c, srec.h: Delete files.