PR22451, strip no longer works on older object files

PR22451, strip no longer works on older object files

Setting SHF_GROUP unconditionally on rel/rela sections associated with
SHF_GROUP sections fails badly with objcopy/strip and ld -r if the
input file SHT_GROUP section didn't specify the rel/rela sections.
This patch rearranges where SHF_GROUP is set for rel/rela sections.

	PR 22451
	PR 22460
	* elf.c (_bfd_elf_init_reloc_shdr): Delete "sec_hdr" parameter
	and leave rel_hdr->sh_flags zero.  Update calls.
	(bfd_elf_set_group_contents): Check input rel/rela SHF_GROUP
	flag when !gas before adding rel/rela section to group.  Set
	output rel/rela SHF_GROUP flags.