refactor(sdk-logs): remove wrapper Promise in _flushOneBatch()

[cjihrig]

Which problem is this PR solving?

BatchLogRecordProcessorBase creates an extra wrapper Promise on each call to _flushOneBatch().

Fixes # N/A

Short description of the changes

This commit removes the extra wrapper Promise and directly returns the callWithTimeout() Promise.

Type of change

Performance refactor

How Has This Been Tested?

• Test suite

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.39%. Comparing base (9a55716) to head (fc1970d).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6253      +/-   ##
==========================================
- Coverage   95.39%   95.39%   -0.01%     
==========================================
  Files         314      314              
  Lines        9516     9514       -2     
  Branches     2198     2198              
==========================================
- Hits         9078     9076       -2     
  Misses        438      438              

Files with missing lines	Coverage Δ
...sdk-logs/src/export/BatchLogRecordProcessorBase.ts	92.92% <100.00%> (-0.15%)	⬇️

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