Uninstalls all packages not specified in Pipfile.lock.

def clean(ctx, state, dry_run=False, bare=False, user=False):
    """Uninstalls all packages not specified in Pipfile.lock."""
    from ..core import do_clean
    do_clean(ctx=ctx, three=state.three, python=state.python, dry_run=dry_run,
             system=state.system)