No sanitize pip

[sivel]

An alternative to #645

This PR just makes no attempt at deduping anything, and removes the sanitization function completely

A few notes about this PR:

1. The --sanitize option still exists, but is hidden, and it does nothing.
2. As a result of making --sanitize a noop, the "default" screen format has changed, to more closely match what --sanitize displayed
3. EXCLUDE_REQUIREMENTS only applied to pip before, simply because sanitize_requirements was only ever used for pip, but it now applies to system as well. We could make EXCLUDE_REQUIREMENTS keyed, and separate them, or put it behind an explicit toggle to the function call
4. This may push errors down deeper, as we don't care what the line is, so it would just be passed on to pip