Fixes to various issues reported by pyflakes

Pyflake is a python (2) source checker. This patch fixes various
(mostly trivial) errors and warnings it reports.

Change-Id: Ia35c5ac61751b927814cf693994c632c412386ea

contrib/ast-db-manage/config/versions/4c573e7135bd_fix_tos_field_types.py

@@ -11,7 +11,6 @@ revision = '4c573e7135bd'
 down_revision = '28887f25a46f'
 
 from alembic import op
-from alembic import context
 import sqlalchemy as sa
 from sqlalchemy.dialects.postgresql import ENUM
 

contrib/ast-db-manage/config/versions/5139253c0423_make_q_member_uniqueid_autoinc.py

@@ -33,7 +33,6 @@ import sqlalchemy as sa
 
 
 def upgrade():
-    context = op.get_context()
     # Was unable to find a way to use op.alter_column() to add the unique
     # index property.
     op.drop_column('queue_members', 'uniqueid')