[gdbserver] Garbage collect unused dependency-tracking Makefile variables.

[gdbserver] Garbage collect unused dependency-tracking Makefile variables.

These used to be necessary for manual rule dependency tracking.
Nothing uses them anymore.  (regdat_sh is still needed.)

gdb/gdbserver/
2013-09-06  Pedro Alves  <palves@redhat.com>

	* Makefile.in (gdb_proc_service_h, regdef_h, regcache_h)
	(signals_def, signals_h, ptid_h, ax_h, agent_h, linux_btrace_h)
	(linux_osdata_h, vec_h, gdb_vecs_h, host_defs_h, libiberty_h)
	(server_h, gdbthread_h, linux_low_h, linux_ptrace_h)
	(gdb_thread_db_h, linux_procfs_h, lynx_low_h, nto_low_h)
	(mips_linux_watch_h, i386_low_h, win32_low_h): Delete.