Fix thread-safety when shutdown.

[owent]

Signed-off-by: owent admin@owent.net

Fixes #1976

Changes

Please provide a brief description of the changes here.

• Do not reset curl handle and just wake background thread to finish the removing.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1977 (5722d77) into main (9d8efaf) will increase coverage by 0.03%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1977      +/-   ##
==========================================
+ Coverage   87.10%   87.12%   +0.03%     
==========================================
  Files         165      165              
  Lines        4596     4596              
==========================================
+ Hits         4003     4004       +1     
+ Misses        593      592       -1     

Impacted Files	Coverage Δ
sdk/src/trace/batch_span_processor.cc	91.48% <0.00%> (+0.78%)	⬆️