Remove unused field service_id from pre-transform spec.
service_id's original purpose was identify the service
that is genarating metric, but this information should
be provided by the source, as a dimension rather
than assigning its value in pre-transform spec.
Change-Id: I223eb2296df438b139e3d9b5aaf4b1b679f70797
Depends-on: I81a35e048e6bd5649c6b3031ac2722be6a309088
Story: 2001815
Task: 12556