Unpin openstack/requirements

Pinning no longer required because of the black list of
oslo.cache 2.1.0 in openstack/requirements.

Related-Bug: #1866008

Change-Id: I9e30f161938c4fe45d91c35d26b308148d082ca8
Depends-On: https://review.opendev.org/#/c/711427/

kolla/common/config.py

@@ -292,14 +292,10 @@ _BASE_OPTS = [
 
 
 SOURCES = {
-    # FIXME(mgoddard): Pinning requirements to
-    # ea42244642c3c091cb4f70917ae8d79af217b6af. This is required to avoid
-    # oslo.cache 2.1.0, which breaks us. See
-    # https://bugs.launchpad.net/kolla-ansible/+bug/1866008.
     'openstack-base': {
-        'type': 'git',
-        'location': 'https://opendev.org/openstack/requirements',
-        'reference': 'ea42244642c3c091cb4f70917ae8d79af217b6af'},
+        'type': 'url',
+        'location': ('$tarballs_base/requirements/'
+                     'requirements-${openstack_branch}.tar.gz')},
     'aodh-base': {
         'type': 'url',
         'location': ('$tarballs_base/aodh/'