fix compiler warnings

[esigo]

Fixes some metrics compiler warnings

Changes

added a virtual dtor, removed unused variables also fixed init order.

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 #1499 (985c0b4) into main (e708de5) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1499      +/-   ##
==========================================
- Coverage   84.76%   84.71%   -0.04%     
==========================================
  Files         155      155              
  Lines        4787     4787              
==========================================
- Hits         4057     4055       -2     
- Misses        730      732       +2     

Impacted Files	Coverage Δ
sdk/src/metrics/state/sync_metric_storage.cc	100.00% <ø> (ø)
...ntelemetry/sdk/metrics/view/attributes_processor.h	100.00% <100.00%> (ø)
sdk/src/metrics/metric_reader.cc	63.89% <100.00%> (ø)
...include/opentelemetry/sdk/common/circular_buffer.h	98.00% <0.00%> (-2.00%)	⬇️
ext/src/http/client/curl/http_client_curl.cc	81.07% <0.00%> (-0.37%)	⬇️

[lalitb]

Thanks.