coff keep_relocs and keep_contents

coff keep_relocs and keep_contents

keep_relocs is set by pe_ILF_save_relocs but not used anywhere in the
coff/pe code.  It is tested by the xcoff backend but not set.

keep_contents is only used by the xcoff backend when dealing with
the .loader section, and it's easy enough to dispense with it there.
keep_contents is set in various places but that's fairly useless when
the contents aren't freed anyway until later linker support functions,
add_dynamic_symbols and check_dynamic_ar_symbols.  There the contents
were freed if keep_contents wasn't set.  I reckon we can free them
unconditionally.

	* coff-bfd.h (struct coff_section_tdata): Delete keep_relocs
	and keep_contents.
	* peicode.h (pe_ILF_save_relocs): Don't set keep_relocs.
	* xcofflink.c (xcoff_get_section_contents): Cache contents.
	Return the contents.  Update callers.
	(_bfd_xcoff_canonicalize_dynamic_symtab): Don't set
	keep_contents for .loader.
	(xcoff_link_add_dynamic_symbols): Free .loader contents
	unconditionally.
	(xcoff_link_check_dynamic_ar_symbols): Likewise.