Prevent spurious revision of Calendar objects.
Prevent spurious revision of Calendar objects.

Currently, transaction records for calendars are committed every time the
last_synced field is updated, which is not correct. Fix this.

nylas/sync-engine,jobscore/sync-engine,nylas/sync-engine,nylas/sync-engine,closeio/nylas,jobscore/sync-engine,jobscore/sync-engine,closeio/nylas,closeio/nylas,jobscore/sync-engine,closeio/nylas,nylas/sync-engine