Remove confusing implicit options handling

This code is supposed to allow

  depends_on "foo" => "with-bar"

to work when foo has only a "without-bar" option.

The options system was not designed to support this. Unfortunately, it
was bolted on anyway. The implementation is extremely difficult to
understand, and it only works for certain types of options, which is
confusing from a user's point of view. Luckily, no formulae in core or
the official taps rely on the behavior in order to function.

It is hindering progress in improving this code, so I am removing it.