Merge keeps alone CREATE and DELETE

[AlexeyBarabash]

We met the situation when [CREATE, UPDATE] were merged to [CREATE], which was then ignored because local object had been existed.
This PR makes CREATE and DELETE records stays alone to prevent such ignoring. So only UPDATE records of the same object id are merged.

STR for brave-core brave-syncer branch:

1. DeviceA: create folderA in bookmarks
2. DeviceA: create bookmarks of brave://bookmarks, brave://sync, brave://inspect, all in Bookmarks Bar folder
3. DeviceA: enable sync and copy code words
4. DeviceB: join sync chain with words from pt.3
5. DeviceB: As soon as bookmarks from DeviceA appear , move 3 bookmarks into folderA
6. Actual on DeviceA: bookmark will not be moved
   Expected on DeviceA: bookmarks should be moved.