Remove deprecated batch_size parameter from _bulk

[andrross]

Related Issues

Resolves #14283

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

✅ Gradle check result for b06dee1: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 72.40%. Comparing base (2d42bd0) to head (b06dee1).
Report is 29 commits behind head on main.

Files with missing lines	Patch %	Lines
...n/java/org/opensearch/action/bulk/BulkRequest.java	0.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #17801      +/-   ##
============================================
+ Coverage     72.39%   72.40%   +0.01%     
- Complexity    66066    66092      +26     
============================================
  Files          5358     5358              
  Lines        306500   306490      -10     
  Branches      44409    44408       -1     
============================================
+ Hits         221888   221914      +26     
+ Misses        66474    66441      -33     
+ Partials      18138    18135       -3     

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