Remove redundant ClusterManagerThrottlingMetricsCollector

[khushbr]

Is your feature request related to a problem? Please provide an existing Issue # , or describe.
#514

Describe the solution you are proposing
Remove the redundant ClusterManagerThrottlingMetricsCollector, the throttling metrics are available via the stats API.

Additional context
More details available at opensearch-project/OpenSearch#479

Check List

• Backport Labels added.
• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Merging #582 (192e2d6) into main (951df93) will increase coverage by 0.05%.
The diff coverage is n/a.

❗ Current head 192e2d6 differs from pull request most recent head d23d5c1. Consider uploading reports for the commit d23d5c1 to get more accurate results

@@             Coverage Diff              @@
##               main     #582      +/-   ##
============================================
+ Coverage     69.22%   69.28%   +0.05%     
+ Complexity      372      371       -1     
============================================
  Files            45       44       -1     
  Lines          2697     2689       -8     
  Branches        172      172              
============================================
- Hits           1867     1863       -4     
+ Misses          727      723       -4     
  Partials        103      103              

Files	Coverage Δ
...performanceanalyzer/PerformanceAnalyzerPlugin.java	76.69% <ø> (-0.23%)	⬇️
.../collectors/ClusterManagerServiceEventMetrics.java	74.17% <ø> (-1.33%)	⬇️
...org/opensearch/performanceanalyzer/util/Utils.java	92.10% <ø> (-0.21%)	⬇️

[opensearch-trigger-bot]

The backport to 1.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-1.x 1.x
# Navigate to the new working tree
cd .worktrees/backport-1.x
# Create a new branch
git switch --create backport/backport-582-to-1.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 9e2b749d317d2cedd98b847f09c7f31f7c94c765
# Push it to GitHub
git push --set-upstream origin backport/backport-582-to-1.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-1.x

Then, create a pull request where the base branch is 1.x and the compare/head branch is backport/backport-582-to-1.x.