Drop usage of importlib_metadata

This is follow-up of b7fe561d09 and use
TypeError caused by the interface change as the key, instead of python
versions, which may work better for distributions with own feature
backports.

Change-Id: I84113cf1dc4de0481c9878a83e2dcd99a8fe69b9

neutron/conf/db/migration_cli.py

@@ -10,22 +10,26 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import sys
+from importlib.metadata import entry_points
 
 from oslo_config import cfg
 
 from neutron._i18n import _
 
-if sys.version_info < (3, 10, 0):
-    from importlib_metadata import entry_points
-else:
-    from importlib.metadata import entry_points
 
 MIGRATION_ENTRYPOINTS = 'neutron.db.alembic_migrations'
-migration_entrypoints = {
-    entrypoint.name: entrypoint
-    for entrypoint in entry_points(group=MIGRATION_ENTRYPOINTS)
-}
+
+try:
+    migration_entrypoints = {
+        entrypoint.name: entrypoint
+        for entrypoint in entry_points(group=MIGRATION_ENTRYPOINTS)
+    }
+except TypeError:
+    # For python < 3.10
+    migration_entrypoints = {
+        entrypoint.name: entrypoint
+        for entrypoint in entry_points()[MIGRATION_ENTRYPOINTS]
+    }
 
 INSTALLED_SUBPROJECTS = list(migration_entrypoints)
 

requirements.txt

@@ -56,6 +56,3 @@ python-designateclient>=2.7.0 # Apache-2.0
 os-vif>=3.1.0 # Apache-2.0
 futurist>=1.2.0 # Apache-2.0
 tooz>=1.58.0 # Apache-2.0
-
-# TODO(tkajinam): Remove importlib_metadata when python 3.9 support is dropped
-importlib_metadata>=3.6;python_version<"3.10" # Apache-2.0