This flag was only used for ReviewDb updates, but ReviewDb is gone.
For NoteDb updates to all changes are written in a single batch ref
update, so parallelization is not used and this option was ignored.
Change-Id: I8d1dfe6ef31d788e2dc250cb40db8c4bc52b3c6b
Signed-off-by: Edwin Kempin <ekempin@google.com>