[DPE-4130] Remove workarounds for removing the OpenSearch application (…

…#317)

## Issue

#243

## Solution

The issue itself could not be reproduced with the current main branch
(revision 95 in channel 2/edge). It was presumably fixed with
#312. This PR adds
integration test coverage.

tests/integration/ha/test_backups.py

@@ -574,9 +574,6 @@ async def test_restore_to_new_cluster(
     """
     app = (await app_name(ops_test) or APP_NAME) if deploy_type == "small" else "main"
     logging.info("Destroying the application")
-    for machine in ops_test.model.state.machines.values():
-        # Needed due to canonical/opensearch-operator#243
-        await machine.destroy(force=True)
     # Now, remove the applications
     await asyncio.gather(
         ops_test.model.remove_application(S3_INTEGRATOR, block_until_done=True),