Remove check for protobuf.. using flatbuffers instead

Change-Id: Ib239daadf0b5012054c0e8992f0c18f04ad5b1cc
Reviewed-on: http://review.couchbase.org/42571
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>