Remove importlib-metadata from requirements

We don't need it anymore as we don't support python < 3.8
Also it was removed from global requirements so it breaks the
requirements check.

Change-Id: Ic558c0a55aff8a0a4f762177a7188069f2baa1fe

cinder/backup/drivers/gcs.py

@@ -27,16 +27,10 @@ Server-centric flow is used for authentication.
 """
 
 import base64
+import importlib.metadata as importlib_metadata
 import io
 import os
 
-try:
-    # For python 3.8 and later
-    import importlib.metadata as importlib_metadata
-except ImportError:
-    # For everyone else
-    import importlib_metadata
-
 try:
     from google.auth import exceptions as gexceptions
     from google.oauth2 import service_account

requirements.txt

@@ -7,7 +7,6 @@ decorator>=4.4.2 # BSD
 eventlet>=0.30.1,!=0.32.0 # MIT
 greenlet>=0.4.16 # MIT
 httplib2>=0.18.1 # MIT
-importlib_metadata>=3.1.1 # Apache-2.0
 iso8601>=0.1.12 # MIT
 jsonschema>=3.2.0 # MIT
 keystoneauth1>=4.2.1 # Apache-2.0