Only show delegates you didn't select already in vote form

[ginacontrino]

Expected behaviour

When I try to vote/unvote delegates and I select a delegate, the selected delegate should not appear anymore in the search

Actual behaviour

When I try to vote/unvote delegates and I select a delegate, the selected delegate still appears in the search when I search for more, which can cause accidental removal of the selected delegates (reselecting will remove the delegate again)

Steps to reproduce

• Go to "VOTE"
• Select a delegate
• Then search for the same delegate again