Remove db SQL Schema Downgrades

Downgrade methods are supposed to be removed following a cross project
spec approved by TC https://review.openstack.org/#/c/152337/

Change-Id: I148f50211fe14bbc4cf22e3312258fc7460119ab
Partially-implements: blueprint remove-schema-downgrades

cloudkitty/db/sqlalchemy/alembic/script.py.mako

@@ -16,7 +16,3 @@ ${imports if imports else ""}
 
 def upgrade():
     ${upgrades if upgrades else "pass"}
-
-
-def downgrade():
-    ${downgrades if downgrades else "pass"}

cloudkitty/db/sqlalchemy/alembic/versions/2ac2217dcbd9_added_support_for_meta_collector.py

@@ -20,7 +20,3 @@ def upgrade():
         sa.Column('service', sa.String(length=255), nullable=False),
         sa.Column('collector', sa.String(length=255), nullable=False),
         sa.PrimaryKeyConstraint('service'))
-
-
-def downgrade():
-    op.drop_table('service_to_collector_mappings')

cloudkitty/db/sqlalchemy/alembic/versions/385e33fef139_added_priority_to_modules_state.py

@@ -18,7 +18,3 @@ def upgrade():
     op.add_column(
         'modules_state',
         sa.Column('priority', sa.Integer(), nullable=True))
-
-
-def downgrade():
-    op.drop_column('modules_state', 'priority')

cloudkitty/db/sqlalchemy/alembic/versions/464e951dc3b8_initial_migration.py

@@ -26,8 +26,3 @@ def upgrade():
         sa.Column('name', sa.String(length=255), nullable=False),
         sa.Column('state', sa.Boolean(), nullable=False),
         sa.PrimaryKeyConstraint('name'))
-
-
-def downgrade():
-    op.drop_table('modules_state')
-    op.drop_table('states')

cloudkitty/db/sqlalchemy/migration.py

@@ -27,11 +27,6 @@ def upgrade(revision):
     return migration.upgrade(config, revision)
 
 
-def downgrade(revision):
-    config = migration.load_alembic_config(ALEMBIC_REPO)
-    return migration.downgrade(config, revision)
-
-
 def version():
     config = migration.load_alembic_config(ALEMBIC_REPO)
     return migration.version(config)