Remove (dead-code) native core file sniffers on Linux targets

Remove (dead-code) native core file sniffers on Linux targets

Since Andreas Arnez' recent patch series, all Linux targets install
gdbarch_iterate_over_regset_sections routines.  This means that on
Linux native targets, old-style core sniffers are never used.

Most Linux targets haven't been using such sniffers for a long time
anyway, but a couple remain: ia64 and sparc use core-regset.o, and
m68k installs its own core_fns.  All this is now dead code, which
this commit removes.

gdb/
2014-11-28  Ulrich Weigand  <uweigand@de.ibm.com>

	* config/ia64/linux.mh (NATDEPFILES): Remove core-regset.o.
	* config/sparc/linux.mh (NATDEPFILES): Likewise.
	* config/sparc/linux64.mh (NATDEPFILES): Likewise.
	* m68klinux-nat.c (fetch_core_registers): Remove.
	(linux_elf_core_fns): Remove.
	(_initialize_m68k_linux_nat): Do not call deprecated_add_core_fns.