Remove description of 'downgrade' for ironic-dbsync

This commit removes a description of 'downgrade' option for
ironic-dbsync. Because 'downgrade' is deprecated from following patch:
I048bd73243d03b03080255c7cfeb53043f10acc5

Change-Id: Ic634dd3122db8f00f98d29d786ad3995b2aeb359

doc/source/cmds/ironic-dbsync.rst

@@ -4,7 +4,7 @@ ironic-dbsync
 
 The :command:`ironic-dbsync` utility is used to create the database schema
 tables that the ironic services will use for storage. It can also be used to
-upgrade (or downgrade) existing database tables when migrating between
+upgrade existing database tables when migrating between
 different versions of ironic.
 
 The `Alembic library <http://alembic.readthedocs.org>`_ is used to perform
@@ -44,7 +44,7 @@ run the following::
 
   Show the program's version number and exit.
 
-.. option:: upgrade, downgrade, stamp, revision, version, create_schema
+.. option:: upgrade, stamp, revision, version, create_schema
 
   The :ref:`command <dbsync_cmds>` to run.
 
@@ -100,26 +100,6 @@ An example of creating database tables with the most recent version::
 
   ironic-dbsync --config-file=/etc/ironic/ironic.conf create_schema
 
-downgrade
----------
-
-.. program:: downgrade
-
-.. option:: -h, --help
-
-  Show help for downgrade and exit.
-
-.. option:: --revision <REVISION>
-
-  The revision number you want to downgrade to.
-
-This command will revert existing database tables to a previous version.
-The version can be specified with the :option:`--revision` option.
-
-An example of downgrading to table versions at revision 2581ebaf0cb2::
-
-  ironic-dbsync --config-file=/etc/ironic/ironic.conf downgrade --revision 2581ebaf0cb2
-
 revision
 --------
 

ironic/cmd/dbsync.py

@@ -95,7 +95,7 @@ def main():
     # this is hack to work with previous usage of ironic-dbsync
     # pls change it to ironic-dbsync upgrade
     valid_commands = set([
-        'upgrade', 'downgrade', 'revision',
+        'upgrade', 'revision',
         'version', 'stamp', 'create_schema',
     ])
     if not set(sys.argv) & valid_commands:

ironic/db/sqlalchemy/alembic/README

@@ -10,7 +10,3 @@ Upgrade can be performed by:
 $ ironic-dbsync - for backward compatibility
 $ ironic-dbsync upgrade
 # ironic-dbsync upgrade --revision head
-
-Downgrading db:
-$ ironic-dbsync downgrade
-$ ironic-dbsync downgrade --revision base

ironic/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"}