Revert "makefile changes for gcm javadocs"

This reverts commit 5f9922d7c3bce158e4c7a58929d4075e7c91e32e.
Disabled droiddoc for online-gcm-ref so that `make sdk` works.
Fixed protobuf dependency issue.

Change-Id: I7bab5c33937d2cd5ee020dc6fd6edbb28ed86560