Merge branch 'fl-18932-revoke-button' into 'master'

Revoke button in Applications Settings underlines on hover

## What does this MR do?
Removes the `btn-link` class from the "Revoke" button

## Why was this MR needed?
The button was being underlined on hover and it shouldn't.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
fixes #18932

See merge request !6522

CHANGELOG

@@ -3,6 +3,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.13.0 (unreleased)
   - Speed-up group milestones show page
   - Fix robots.txt disallowing access to groups starting with "s" (Matt Harrison)
+  - Revoke button in Applications Settings underlines on hover.
 
 v 8.12.2 (unreleased)
   - Fix Import/Export not recognising correctly the imported services.

app/views/doorkeeper/authorized_applications/_delete_form.html.haml

@@ -6,4 +6,4 @@
   
 = form_tag path do
   %input{:name => "_method", :type => "hidden", :value => "delete"}/
-  = submit_tag 'Revoke', onclick: "return confirm('Are you sure?')", class: 'btn btn-link btn-remove btn-sm'
+  = submit_tag 'Revoke', onclick: "return confirm('Are you sure?')", class: 'btn btn-remove btn-sm'