chore: remove unused default argument in Tracer

[Flarna]

A Tracer is always created by a TracerProvider and this one always passes it's config
therefore no need to default in constructor.

[codecov-io]

Codecov Report

Merging #913 into master will decrease coverage by 1.56%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #913      +/-   ##
==========================================
- Coverage   94.49%   92.92%   -1.57%     
==========================================
  Files         246      246              
  Lines       10898    11159     +261     
  Branches     1044     1091      +47     
==========================================
+ Hits        10298    10370      +72     
- Misses        600      789     +189     

Impacted Files	Coverage Δ
packages/opentelemetry-tracing/src/Tracer.ts	100.00% <100.00%> (+1.78%)	⬆️
...entelemetry-core/test/context/B3Propagator.test.ts	45.53% <0.00%> (-54.47%)	⬇️
packages/opentelemetry-core/test/utils/url.test.ts	50.00% <0.00%> (-50.00%)	⬇️
...pentelemetry-core/test/internal/validators.test.ts	50.00% <0.00%> (-50.00%)	⬇️
...elemetry-core/test/trace/spancontext-utils.test.ts	55.55% <0.00%> (-44.45%)	⬇️
...lemetry-core/test/trace/ProbabilitySampler.test.ts	61.70% <0.00%> (-38.30%)	⬇️
...s/opentelemetry-core/test/trace/tracestate.test.ts	65.06% <0.00%> (-34.94%)	⬇️
...ckages/opentelemetry-core/test/platform/id.test.ts	66.66% <0.00%> (-33.34%)	⬇️
...ntelemetry-core/test/trace/NoRecordingSpan.test.ts	71.42% <0.00%> (-28.58%)	⬇️
...ages/opentelemetry-plugin-http/test/utils/utils.ts	33.33% <0.00%> (-26.67%)	⬇️
... and 51 more

[dyladan]

Tracers should not be created manually anyway so I think this is a good change.

[vmarchaud]

👍

[mayurkale22]

LGTM