As a minor cleanup remove the (r)index defines from include/string.h as

they are only used internally in a few places.  Rename all uses that
occur in GLIBC.

	* hurd/path-lookup.c (file_name_path_scan): Rename index to strchr.
	* include/string.h (index): Remove define.
	(rindex): Likewise.
	* misc/getttyent.c (__getttyent): Rename index to strchr.
	* misc/ttyslot.c (ttyslot): Rename rindex to strrchr.
	* sunrpc/rpc_main.c (mkfile_output): Likewise.