use python dates for request revisions, plus some cleanup

atst/models/request.py

@@ -8,6 +8,7 @@ from atst.models import Base
 from atst.models.types import Id
 from atst.models.request_status_event import RequestStatus
 from atst.utils import deep_merge, first_or_none
+from atst.models.request_revision import RequestRevision
 
 
 def map_properties_to_dict(properties, instance):

atst/models/request_revision.py

@@ -1,7 +1,5 @@
-import pendulum
 from sqlalchemy import (
     Column,
-    func,
     ForeignKey,
     String,
     Boolean,
@@ -10,8 +8,6 @@ from sqlalchemy import (
     BigInteger,
     Sequence,
 )
-from sqlalchemy.types import DateTime
-from sqlalchemy.dialects.postgresql import JSONB
 from sqlalchemy.orm import relationship
 
 from atst.models import Base