Remove is_relocatable_executable from backend code

With the removal of symbian support, most targets no longer or never
did set is_relocatable_executable.  Remove the backend support that is
no longer relevant.

	* elf32-arm.c (record_arm_to_thumb_glue, elf32_arm_create_thumb_stub),
	(elf32_arm_final_link_relocate, elf32_arm_check_relocs),
	(elf32_arm_adjust_dynamic_symbol, allocate_dynrelocs_for_symbol),
	(elf32_arm_output_arch_local_syms): Remove is_relocatable_executable
	code and comments.
	* elf32-csky.c (csky_elf_adjust_dynamic_symbol): Likewise.
	* elfnn-aarch64.c (elfNN_aarch64_final_link_relocate): Likewise.
	* elfnn-kvx.c (elfNN_kvx_final_link_relocate): Likewise.
	* elfxx-mips.c (count_section_dynsyms): Likewise.