[Enhancement] Remove synchronized from deleteTopic to speed up topic deletion.

### Before Creating the Enhancement Request

- [x] I have confirmed that this should be classified as an enhancement rather than a bug/feature.

### Summary

Remove synchronized from deleteTopic to speed up topic deletion.

### Motivation

Remove synchronized from deleteTopic to speed up topic deletion.

### Describe the Solution You'd Like

Remove synchronized from deleteTopic to speed up topic deletion.

### Describe Alternatives You've Considered

No

### Additional Context

_No response_

The issue identifies deleteTopic as the entry point but names no file or test. Inspect its Java implementation and related concurrency behavior first; done means topic deletion is faster without synchronized while remaining correct under concurrent operations.

Written by the indexing model from the issue text.