Don't pluck IDs in AutocompleteUsersFinder
Don't pluck IDs in AutocompleteUsersFinder

We can instead just use a UNION. This removes the need for plucking
hundreds if not thousands of IDs into memory when a project has many
members.

axilleas/gitlabhq,jirutka/gitlabhq,dreampet/gitlab,axilleas/gitlabhq,mmkassem/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,stoplightio/gitlabhq,jirutka/gitlabhq,jirutka/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,axilleas/gitlabhq,axilleas/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git,dreampet/gitlab,dreampet/gitlab,mmkassem/gitlabhq,iiet/iiet-git,iiet/iiet-git,stoplightio/gitlabhq