db: drop __mapper_args__ that cause SQLAlchemy deprecation warnings

We don't really need them. There were only few uses left, and we seem to be
using .order_by() in all places where we really care about the ordering.

Gets rid of

<string>:2
  <string>:2: SADeprecationWarning: Mapper.order_by is deprecated.Use Query.order_by() in order to affect the ordering of ORM result sets.

kallithea/model/db.py

@@ -706,7 +706,6 b' class UserApiKeys(Base, BaseDbModel):'
         Index('uak_api_key_expires_idx', 'api_key', 'expires'),
         _table_args_default_dict,
     )
-    __mapper_args__ = {}
 
     user_api_key_id = Column(Integer(), primary_key=True)
     user_id = Column(Integer(), ForeignKey('users.user_id'), nullable=False)
@@ -728,7 +727,6 b' class UserEmailMap(Base, BaseDbModel):'
         Index('uem_email_idx', 'email'),
         _table_args_default_dict,
     )
-    __mapper_args__ = {}
 
     email_id = Column(Integer(), primary_key=True)
     user_id = Column(Integer(), ForeignKey('users.user_id'), nullable=False)
@@ -758,7 +756,6 b' class UserIpMap(Base, BaseDbModel):'
         UniqueConstraint('user_id', 'ip_addr'),
         _table_args_default_dict,
     )
-    __mapper_args__ = {}
 
     ip_id = Column(Integer(), primary_key=True)
     user_id = Column(Integer(), ForeignKey('users.user_id'), nullable=False)
@@ -1470,7 +1467,6 b' class RepoGroup(Base, BaseDbModel):'
     __table_args__ = (
         _table_args_default_dict,
     )
-    __mapper_args__ = {'order_by': 'group_name'} # TODO: Deprecated as of SQLAlchemy 1.1.
 
     SEP = ' » '