Skip unnecessary shared state updates in safekeepers

[petuhovskiy]

I looked at the metrics from #7768 on staging and it seems that manager does too many iterations. This is probably caused by background job remove_wal.rs which iterates over all timelines and tries to remove WAL and persist control file. This causes shared state updates and wakes up the manager. The fix is to skip notifying about the updates if nothing was updated.

[github-actions]

3108 tests run: 2981 passed, 0 failed, 127 skipped (full report)

---

Code coverage* (full report)

• functions: 31.4% (6449 of 20544 functions)
• lines: 48.3% (49860 of 103260 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
d2a2bb6 at 2024-05-22T23:50:06.813Z :recycle:}