[Chore] Remove unnecessary return statements

[10000-ki]

Description

[Describe what this change achieves]

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)
• Why these changes are required?
• What is the old behavior before changes and new behavior after changes?

Remove unnecessary return statements

• clean up code

Issues Resolved

[List any issues this PR will resolve]

none

Is this a backport? If so, please add backport PR # and/or commits #

Do these changes introduce new permission(s) to be displayed in the static dropdown on the front-end? If so, please open a draft PR in the security dashboards plugin and link the draft PR here

Testing

[Please provide details of testing done: unit testing, integration testing and manual testing]

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• 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

All modified and coverable lines are covered by tests ✅

Project coverage is 65.28%. Comparing base (cfb5525) to head (7879253).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4558      +/-   ##
==========================================
- Coverage   65.30%   65.28%   -0.02%     
==========================================
  Files         317      317              
  Lines       22274    22272       -2     
  Branches     3582     3582              
==========================================
- Hits        14546    14541       -5     
- Misses       5936     5939       +3     
  Partials     1792     1792              

Files	Coverage Δ
...opensearch/security/filter/SecurityRestFilter.java	70.67% <ø> (+0.30%)	⬆️

... and 2 files with indirect coverage changes