Remove list of message groups from api documentation

* These lists can get huge, especially if repeated for many modules
* There is separate api module to list message groups
* Given that api documentation is accessible to all by default,
  it can also leak information that was not meant for public

Change-Id: I46ac1a738ec4dcbd4b4e102cdce14f5633f92399
Merge "Remove list of message groups from api documentation"