ELF sec_info memory leaks

Use the bfd's objalloc memory so we don't need to free anything
attached to elf_section_data sec_info.  Other uses of sec_info that
need to allocate memory already use bfd_alloc.

	* elf-eh-frame.c (_bfd_elf_parse_eh_frame): bfd_alloc sec_info.
	* elf-sframe.c (_bfd_elf_parse_sframe): Likewise.