Get rid of constants.RAPI_ENABLE

This constant is unused, except in qa. Removing it since it's always True.

This patch also removes the unused qa_rapi.PrintRemoteAPIWarning
function, and removes a comment about temporary constants "until we have
cluster parameters".

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>