chore: temporarily revert retries in merge insert

[wjones127]

We believe this may be related to #3798, and so are reverting some of the changes in #3614 for now.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 78.47%. Comparing base (01962ad) to head (13a6b2d).

Files with missing lines	Patch %	Lines
rust/lance/src/dataset/write/merge_insert.rs	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3799      +/-   ##
==========================================
- Coverage   78.59%   78.47%   -0.12%     
==========================================
  Files         274      274              
  Lines      102130   101913     -217     
  Branches   102130   101913     -217     
==========================================
- Hits        80269    79981     -288     
- Misses      18693    18777      +84     
+ Partials     3168     3155      -13     

Flag	Coverage Δ
unittests	78.47% <80.00%> (-0.12%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.