Demote deletion warning, list files (#4688)

Handle test failures like:

```
AssertionError: assert not ['$ts  WARN delete_timeline{tenant_id=X timeline_id=Y}: About to remove 1 files\n']
```

Instead of logging:

```
WARN delete_timeline{tenant_id=X timeline_id=Y}: Found 1 files not bound to index_file.json, proceeding with their deletion
WARN delete_timeline{tenant_id=X timeline_id=Y}: About to remove 1 files
```

For each one operation of timeline deletion, list all unref files with
`info!`, and then continue to delete them with the added spice of
logging the rare/never happening non-utf8 name with `warn!`.

Rationale for `info!` instead of `warn!`: this is a normal operation;
like we had mentioned in `test_import.py` -- basically whenever we
delete a timeline which is not idle.

Rationale for N * (`ìnfo!`|`warn!`): symmetry for the layer deletions;
if we could ever need those, we could also need these for layer files
which are not yet mentioned in `index_part.json`.

---------

Co-authored-by: Christian Schwarz <christian@neon.tech>

test_runner/regress/test_import.py

@@ -149,12 +149,6 @@ def test_import_from_vanilla(test_output_dir, pg_bin, vanilla_pg, neon_env_build
         ".*WARN.*ignored .* unexpected bytes after the tar archive.*"
     )
 
-    # NOTE: delete can easily come before upload operations are completed
-    # https://github.com/neondatabase/neon/issues/4326
-    env.pageserver.allowed_errors.append(
-        ".*files not bound to index_file.json, proceeding with their deletion.*"
-    )
-
     timeline_delete_wait_completed(client, tenant, timeline)
 
     # Importing correct backup works

test_runner/regress/test_remote_storage.py

@@ -598,9 +598,6 @@ def test_timeline_deletion_with_files_stuck_in_upload_queue(
         ".* ERROR .*Error processing HTTP request: InternalServerError\\(timeline is Stopping"
     )
 
-    env.pageserver.allowed_errors.append(
-        ".*files not bound to index_file.json, proceeding with their deletion.*"
-    )
     timeline_delete_wait_completed(client, tenant_id, timeline_id)
 
     assert not timeline_path.exists()