[Backport 2.x] [Snapshot V2] Remove orphan timestamps post create snapshot completion

[opensearch-trigger-bot]

Backport 6020c58 from #16148.

[github-actions]

❌ Gradle check result for 0727abf: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for 0727abf: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 36.00000% with 32 lines in your changes missing coverage. Please review.

Project coverage is 71.65%. Comparing base (06ee966) to head (0727abf).
Report is 2 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...ava/org/opensearch/snapshots/SnapshotsService.java	24.24%	24 Missing and 1 partial ⚠️
...remotestore/RemoteStorePinnedTimestampService.java	58.82%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #16178      +/-   ##
============================================
- Coverage     71.71%   71.65%   -0.07%     
+ Complexity    64825    64729      -96     
============================================
  Files          5279     5279              
  Lines        302913   302963      +50     
  Branches      44066    44072       +6     
============================================
- Hits         217242   217081     -161     
- Misses        67537    67740     +203     
- Partials      18134    18142       +8     

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