Delete the "availableQueryOptions" command on mongos and mongod

As of SERVER-60749 this command will no longer be used internally. Drivers also do not use the command. It apparently was used as an old way to discover whether the remote node supported exhaust queries. But exhaust has been supported for a very long time now, and we are currently relying on the min and max wire version for feature discovery.

We cannot delete the command until after branching for 6.0. This is because node 5.1 and older can still issue it on some internal code paths. After branching for 6.0, it should be safe to delete.