remove getDefaultBound and setCallback from Metric API

[mayurkale22]

Which problem is this PR solving?

• I think getDefaultBound and setCallback are non-compliant methods with specifications.

/cc @dyladan

[dyladan]

Cool they're unimplemented anyways

[codecov-io]

Codecov Report

Merging #793 into master will decrease coverage by 0.14%.
The diff coverage is 98.71%.

@@            Coverage Diff             @@
##           master     #793      +/-   ##
==========================================
- Coverage   94.48%   94.34%   -0.15%     
==========================================
  Files         239      246       +7     
  Lines       10468    10809     +341     
  Branches      998     1034      +36     
==========================================
+ Hits         9891    10198     +307     
- Misses        577      611      +34

Impacted Files	Coverage Δ
packages/opentelemetry-plugin-http/src/http.ts	97.72% <ø> (ø)	⬆️
packages/opentelemetry-plugin-http/src/utils.ts	97.4% <100%> (+0.14%)	⬆️
...es/opentelemetry-plugin-express/test/utils.test.ts	100% <100%> (ø)
...ckages/opentelemetry-plugin-express/src/version.ts	100% <100%> (ø)
packages/opentelemetry-plugin-express/src/types.ts	100% <100%> (ø)
...pentelemetry-exporter-prometheus/src/prometheus.ts	90% <100%> (ø)	⬆️
...lemetry-plugin-http/test/functionals/utils.test.ts	99.4% <100%> (+0.03%)	⬆️
packages/opentelemetry-plugin-express/src/utils.ts	95.45% <95.45%> (ø)
...ckages/opentelemetry-plugin-express/src/express.ts	98.85% <98.85%> (ø)
.../opentelemetry-plugin-express/test/express.test.ts	99.14% <99.14%> (ø)
... and 172 more