Merge branch 'remove-transition-prefix' into 'master'

Remove prefixes from transition CSS property

## What does this MR do?
Removes vendor prefixes from the CSS transition property

## Are there points in the code the reviewer needs to double check?
None

## Why was this MR needed?
Reduces unnecessary CSS

## Screenshots (if relevant)
None

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [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)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #21614

See merge request !6093

CHANGELOG

@@ -24,6 +24,7 @@ v 8.12.0 (unreleased)
   - Add `wiki_page_events` to project hook APIs (Ben Boeckel)
   - Remove Gitorious import
   - Fix inconsistent background color for filter input field (ClemMakesApps)
+  - Remove prefixes from transition CSS property (ClemMakesApps)
   - Add Sentry logging to API calls
   - Add BroadcastMessage API
   - Automatically expand hidden discussions when accessed by a permalink !5585 (Mike Greiling)

app/assets/stylesheets/framework/mixins.scss

@@ -9,14 +9,6 @@
   border-radius: $radius;
 }
 
-@mixin transition($transition) {
-  -webkit-transition: $transition;
-  -moz-transition: $transition;
-  -ms-transition: $transition;
-  -o-transition: $transition;
-  transition: $transition;
-}
-
 /**
  * Prefilled mixins
  * Mixins with fixed values

app/assets/stylesheets/framework/selects.scss

@@ -151,7 +151,7 @@
   background-position: right 0 bottom 6px;
   border: 1px solid $input-border;
   @include border-radius($border-radius-default);
-  @include transition(border-color ease-in-out .15s, box-shadow ease-in-out .15s);
+  transition: border-color ease-in-out 0.15s, box-shadow ease-in-out 0.15s;
 
   &:focus {
     border-color: $input-border-focus;

app/assets/stylesheets/pages/search.scss

@@ -80,7 +80,7 @@
 
     .search-icon {
       @extend .fa-search;
-      @include transition(color .15s);
+      transition: color 0.15s;
       -webkit-user-select: none;
       -moz-user-select: none;
       -ms-user-select: none;
@@ -125,7 +125,7 @@
     }
 
     .location-badge {
-      @include transition(all .15s);
+      transition: all 0.15s;
       background-color: $location-badge-active-bg;
       color: $white-light;
     }