chore(instrumentation-grpc): remove unused findIndex() function

[cjihrig]

Which problem is this PR solving?

There is not a problem, but this appears to be unused code.

Fixes N/A

Short description of the changes

This commit removes the findIndex() function. This function appears to be unused and findIndex() is part of the language now.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Ran the test suite

Checklist:

• Followed the style guidelines of this project

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.62%. Comparing base (2a26d08) to head (8de94b1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5372      +/-   ##
==========================================
+ Coverage   94.54%   94.62%   +0.08%     
==========================================
  Files         318      318              
  Lines        8046     8038       -8     
  Branches     1688     1687       -1     
==========================================
- Hits         7607     7606       -1     
+ Misses        439      432       -7     

Files with missing lines	Coverage Δ
...es/opentelemetry-instrumentation-grpc/src/utils.ts	95.55% <ø> (+12.53%)	⬆️

[pichlermarc]

Nice, thanks!