Originally fixed in If708dc98, but this only works for some submit
strategies. For other submit strategies, such as rebase always,
firstly the "rebase" is created which for some legacy reason, also
adds the person who performed the "submit as a reviewer. Then,
that person is added to the attention set. On the other hand,
with "merge if necessary" strategy, there is only one ChangeUpdate,
so the solution in the change above works.
The fix is simple: We can figure out that we're submitting a change
based on the legacy label, and then never add anyone to the attention
set, since all users should anyway be removed when submitting.
Change-Id: I0ce58a66eb3f9987050ea25125e91aa85e621883
be808375ba