chore: remove events subscription v1beta (#13965)

Reverts #13962

See b/421467004

Author: parthea

packages/google-apps-events-subscriptions/.OwlBot.yaml

@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+deep-preserve-regex:
+    - /owl-bot-staging/google-apps-events-subscriptions/v1beta
 deep-copy-regex:
     - source: /google/apps/events/subscriptions/(v.*)/.*-py
       dest: /owl-bot-staging/google-apps-events-subscriptions/$1