Remove --use-first-matching-interpreter misfeature

[Eric-Arellano]

This was a misfeature added to support a Pants use case, which is implemented another way.

This never worked very robustly:

To be clear though, there are many corners this will not work for including mismatching abi (python2.7m vs python2.7mu) when the PEX contains platform specific wheels, etc.

If a user only wants to resolve for one interpreter, they should use --python or the upcoming --python-path.

We don't use a proper deprecation due to #584. We'll call attention to this in the release notes.