Consider changing the Javadoc policy to allow omitting unnecessary param and return tags.

[sebright]

This is related to the discussion in #485 (comment). Javadocs written with the current style (https://github.com/census-instrumentation/opencensus-java/blob/master/CONTRIBUTING.md#javadoc) can sometimes clutter the documentation and hide the most relevant points.

[codefromthecrypt]

Thanks for raising this. You captured my concern succinctly!