When `install_with_build_args` was added in
be96283985,
there were two versions of the method: the default version in the base class that still
used the locking `with_build_args`, and an override in the `Future`
class (for Rubygems 2.0 and up) that yielded without calling
`with_build_args`.
The `with_build_args` version of the method was removed in
8a5b71e3e8
while removing a bunch of the old Rubygems compatibility code.
This commit removes `with_build_args`, since it no longer appears to be
used (the build args are passed as a keyword argument to
`spec.source.install` instead, since
be96283985).
The commit also removes `install_with_build_args` and the conditional
around it, since the method wasn't doing anything different than
`install`, and it had a comment that was no longer accurate.
https://github.com/rubygems/rubygems/commit/ba543a60eb
7394514bde