Duplicate client metrics with semconv v1.26 in otelhttp

[dmathieu]

Closes #6261

[codecov]

Codecov Report

Attention: Patch coverage is 91.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 68.6%. Comparing base (9640704) to head (c19c864).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ion/net/http/otelhttp/internal/semconv/httpconv.go	87.3%	6 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6607     +/-   ##
=======================================
+ Coverage   68.5%   68.6%   +0.1%     
=======================================
  Files        200     200             
  Lines      16781   16872     +91     
=======================================
+ Hits       11500   11585     +85     
- Misses      4935    4939      +4     
- Partials     346     348      +2     

Files with missing lines	Coverage Δ
...entation/net/http/otelhttp/internal/semconv/env.go	93.3% <100.0%> (+1.1%)	⬆️
instrumentation/net/http/otelhttp/transport.go	94.8% <100.0%> (ø)
...ion/net/http/otelhttp/internal/semconv/httpconv.go	87.0% <87.3%> (+<0.1%)	⬆️

... and 1 file with indirect coverage changes