Remove elf_backend_write_core_note

Remove elf_backend_write_core_note

This function was added in 2007 to support powerpc gdb "gcore" writing
32-bit powerpc linux core files on a 64-bit powerpc host, when
PowerPC64 glibc lacked (and still lacks) 32-bit versions of prstatus_t
and prpsinfo_t.  Now that gdb has elfcore_write_linux_prstatus32/64
and elfcore_write_linux_prpsinfo32/64, this linux specific backend
function should disappear.

	* elf-bfd.h (struct elf_backend_data): Remove
	elf_backend_write_core_note.
	* elf.c (elfcore_write_prpsinfo, elfcore_write_prstatus): Don't call
	elf_backend_write_core_note.
	* elf32-arm.c (elf32_arm_nabi_write_core_note): Delete function.
	(elf_backend_write_core_note): Don't define.
	* elf32-ppc.c (ppc_elf_write_core_note): Delete function.
	(elf_backend_write_core_note): Don't define.
	* elf64-ppc.c (ppc64_elf_write_core_note): Delete function.
	(elf_backend_write_core_note): Don't define.
	* elf64-x86-64.c (elf_x86_64_write_core_note): Delete function.
	(elf_backend_write_core_note): Don't define.
	(CORE_HEADER): Don't include.
	* elfxx-aarch64.c (_bfd_aarch64_elf_write_core_note): Delete function.
	* elfxx-aarch64.h (_bfd_aarch64_elf_write_core_note): Delete prototype.
	(elf_backend_write_core_note): Don't define.
	* elfxx-target.h (elf_backend_write_core_note): Don't define.
	(elfNN_bed): Adjust.
	* hosts/x86-64linux.h: Delete file.
	* configure.ac (CORE_HEADER): Delete.
	* configure: Regenerate.
	* config.in: Regenerate.