Use new repository clone button in wikis

Summary

Wikis use an old version of our clone panel:

Improvements

Switch to the new clone button used in projects and snippets:

This will allow us to remove some legacy code which was only used for the old clone panel.

Involved components

After switching, the following code can be removed:

• app/views/shared/_clone_panel.html.haml
  • app/helpers/button_helper.rb: http_clone_button, http_dropdown_description, ssh_clone_button
  • ee/app/helpers/ee/button_helper.rb: overrides for the above methods
• ee/app/views/shared/_kerberos_clone_button.html.haml
  • ee/app/helpers/ee/button_helper.rb: kerberos_clone_button
• qa/qa/page/component/legacy_clone_panel.rb

The new clone button has two implementations as well:

• app/views/projects/buttons/_clone.html.haml (projects)
  • There's also a mobile version in app/views/shared/_mobile_clone_panel.html.haml.
• app/assets/javascripts/vue_shared/components/clone_dropdown.vue (snippets)

It would probably make sense to use the Vue version, although it doesn't have a proper mobile version yet.