Partially revert f490a8d39a12ed2c6b125b3380f08b2d1d43ee7f because we aren't able to
load more than the initially preloaded voters.
We were always trying to load the 1st page of voters.
Also removed the "remove users who changed their vote" logic as it was not properly working in multiple choices polls.
cc @nbianca
* FIX: Fetch last page again if incomplete
The next fetched page number used to increase continuously even if the
last page was incomplete and fetching it again could have new voters.
* FIX: Do not display twice a user who changed vote
A user could appear under two voting options when they changed their
vote because pressing the Load More Voters button updated only the
current option.
