Don't show irrelevant MNs in prover

Previously, proof steps like applyTactic would introduce MNs to the
proof state, with names like {scriptVar231}. This change hides those, as
the user cannot type them anyway.

If they are used in a later assumption, then they will be shown anyway.
Merge pull request #1450 from david-christiansen/dont-show-mn-in-proof

Don't show irrelevant MNs in prover