1. Open the track's automation Lanes. In the lanes, you'll see the "real" envelopes that are in use.
2. Select Clips in the Edit Filter, and drag over the part of the track containing the orphaned envelopes (do not select the entire track).
3. Choose Edit > Cut Special, check only Track/Bus Automation, then click OK.
If you want to delete all envelopes in a track, orphaned and active, select the track then do step 3.