Fix runners-up candidacy submission check in council

[kianenigma]

same issue as: https://github.com/paritytech/substrate/pull/4429/files

• Tests already existed; yet they also worked with the wrong binary search since the container to search was just one element. I reviewed all leftover of the binary_seach_xxx in that file and they only apply to members and candidates who are actually sorted by account id; This should close this whole issue.
• With or without this update, in the next Kusama term change the candidate list should be cleaned. Luckily the phragmen implementation also ignores (kinda by luck; needs issue to be cleaned) dupe candidates so we should be fine.

[shawntabrizi]

This has a broken test @kianenigma @gavofyork

[kianenigma]

should be fixed with #4594