Roll WITHOUT_ELFTOOLCHAIN_TOOLS into WITHOUT_TOOLCHAIN

The option was added only to ease the transition from GNU Binutils to
ELF Tool Chain tools, and that process is now complete (for the viable
replacements). Noting the removal in UPDATING is sufficient as we have
not shipped a release with the option.

Reviewed by: brooks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D3240