ACCUMULO-1961 Re-apply inadvertently dropped 4abb3f1 to master branch

  Fixes trivial warnings and broken javadocs which have been recently
  introduced. Specifically, removes references to private and
  package-private (default) classes in public javadoc comments (internal
  details aren't relevant to the API and subject to change). Another
  common warning was unused imports and javadoc param tags that refer to
  non-existent parameters.

  Commits against the following JIRA issues introduced these:
  ACCUMULO-1948, ACCUMULO-1974, ACCUMULO-2021, ACCUMULO-2136,
  ACCUMULO-2322, ACCUMULO-2334, ACCUMULO-2350