Follow-up from "Add deploy keys support for Protected tags"

The following discussion from !110047 (merged) should be addressed:

• @jerasmus started a discussion: (+1 comment)

  Note to reviewer: most changes in this file is code that was moved from ee/app/assets/javascripts/protected_tags/protected_tag_create.js so that we can get rid of the EE code as there's no reason for us to have the two separate files. A full refactor would have been ideal but it falls out of scope of this MR, I believe consolidating the CE/EE code is a move in the right direction.

Also see this note in the related MR.