Reduce public exposure of noops

[cijothomas]

Part of #1712
A lot of others noops are used by opentelemetry-sdk. I think sdk can find different ways to handle this. Will explore that later.

[lalitb]

Not sure if I am interpreting correct, but seems the specs says they should be available(exposed?) in the API surface - https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/noop.md. Though in general agree to remove if they won't be ever used in libraries.

[cijothomas]

Not sure if I am interpreting correct, but seems the specs says they should be available(exposed?) in the API surface - https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/noop.md. Though in general agree to remove if they won't be ever used in libraries.

It could be added back to public api of opentelemetry, if necessary. As long as all the APIs are no-op, even without exposing the no-op as-is, we should be good.

note: I don't think it is extra risky to expose the noops anyway, as the traits are anyway public!