DO NOT MERGE. Remove service component for KLP.

1) As discussed, lack of internal clients -> remove SyncService
component from KLP. This CL reverts that addition.
2) Also includes javadoc cleanup of existing API.
3) Fix naming of allowMetered() -> disallowMetered() in API
4) Removed one-off sync in the future, as it doesn't make sense
for sync adapters.

Change-Id: I1b17094e6edafb2955cdfb99f39b44274fbe86f9