db: remove enabled/disabled from ReposListOptions
Created by: keegancsmith
All repos are enabled, so these fields have been noops since 3.4. Had to
update all call sites for listing repos. If it specified disabled: true
and
not enabled: true
we know the result set is empty so the code is
updated. Otherwise the filter is a noop so we just remove specifying the
fields.
Part of https://github.com/sourcegraph/sourcegraph/issues/3971