remove redundant instrumentations != null checks

[SimonCropp]

Fixes #
Design discussion issue #

Changes

Please provide a brief description of the changes here.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[TimothyMothra]

LGTM.
Need to sync with main.

[SimonCropp]

Need to sync with main.

done

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.37%. Comparing base (36b777b) to head (961e1b4).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6091      +/-   ##
==========================================
- Coverage   86.39%   86.37%   -0.02%     
==========================================
  Files         257      257              
  Lines       11639    11622      -17     
==========================================
- Hits        10055    10039      -16     
+ Misses       1584     1583       -1     

Files with missing lines	Coverage Δ
src/OpenTelemetry/Logs/LoggerProviderSdk.cs	92.55% <ø> (-0.31%)	⬇️
src/OpenTelemetry/Metrics/MeterProviderSdk.cs	93.19% <ø> (-0.12%)	⬇️
src/OpenTelemetry/Trace/TracerProviderSdk.cs	99.65% <ø> (+0.32%)	⬆️