Remove usage of bootstrap "collapse" within mirror helper scripts

The bootstrap .collapse() method and associated event handlers are used extensively within the following related scripts:

• app/assets/javascripts/mirrors/mirror_repos.js
• app/assets/javascripts/mirrors/ssh_mirror.js
• ee/app/assets/javascripts/pages/projects/settings/repository/show/ee_mirror_repos.js

These appear to show and hide form elements with the collapse function based on user input in a text field.

Since we are endeavoring to remove bootstrap's "collapse" function from our codebase, these must be refactored to work without it. The animation that bootstrap provides when toggling between .collapse, .collapse.show, and .collapsing could be replaced with our own CSS animation or the expand/collapse animation can be omitted altogether.