Disable BINUTILS by default on amd64

The retirement of obsolete binutils 2.17.50 has been in progress for
quite some time. All tools other than GNU as were removed prior to this
commit, and it was built only on amd64 - installed as /usr/bin/as, and
used as a bootstrap tool.

The amd64 exp-run has completed and failures have now been addressed in
the individual ports, so disable it by default.

PR: 233611, 205250 [exp-run]
Sponsored by: The FreeBSD Foundation