onions: switch bc2 over to new onion table, drop mirrors table

fixes: #4

app/cli/db.py

@@ -9,7 +9,7 @@ from app import app
 from app.extensions import db
 from app.models.base import Group, MirrorList
 from app.models.bridges import Bridge, BridgeConf
-from app.models.mirrors import Mirror, Origin, Proxy
+from app.models.mirrors import Origin, Proxy
 from app.models.alarms import Alarm, AlarmState
 
 if TYPE_CHECKING:
@@ -23,7 +23,6 @@ models = {
     "alarm": Alarm,
     "group": Group,
     "list": MirrorList,
-    "mirror": Mirror,
     "origin": Origin,
     "proxy": Proxy
 }