Remove unused extends from some CSS pages

Dropdown one not needed
col-lg one I inlined classes
Others I inlined relevant rules

app/assets/javascripts/notes/components/note_attachment.vue

@@ -24,7 +24,7 @@ export default {
       target="_blank"
       rel="noopener noreferrer"
     >
-      <img :src="attachment.url" class="note-image-attach" />
+      <img :src="attachment.url" class="note-image-attach col-lg-4" />
     </a>
     <div class="attachment">
       <a

app/assets/stylesheets/pages/login.scss

@@ -179,8 +179,9 @@
   }
 
   input[type='submit'] {
-    @extend .btn-block;
     margin-bottom: 0;
+    display: block;
+    width: 100%;
   }
 
   .devise-errors {

app/assets/stylesheets/pages/merge_requests.scss

@@ -236,8 +236,8 @@ $tabs-holder-z-index: 250;
   }
 
   .label-branch {
-    @extend .ref-name;
-
+    @include gl-font-monospace;
+    font-size: 95%;
     color: $gl-text-color;
     font-weight: normal;
     overflow: hidden;

app/assets/stylesheets/pages/note_form.scss

@@ -48,7 +48,6 @@
 }
 
 .note-image-attach {
-  @extend .col-lg-4;
   margin-left: 45px;
   float: none;
 }

app/assets/stylesheets/pages/notifications.scss

 .notification-list-item {
-  .dropdown-menu {
-    @extend .dropdown-menu-right;
-  }
-
   @include media-breakpoint-down(sm) {
     .notification-dropdown {
       width: 100%;

app/views/events/event/_note.html.haml

@@ -22,7 +22,7 @@
     - if note.attachment.url
       - if note.attachment.image?
         = link_to note.attachment.url, target: '_blank' do
-          = image_tag note.attachment.url, class: 'note-image-attach'
+          = image_tag note.attachment.url, class: 'note-image-attach col-lg-4'
       - else
         = link_to note.attachment.url, target: '_blank', class: 'note-file-attach' do
           = sprite_icon("paperclip")

app/views/shared/notes/_note.html.haml

@@ -69,7 +69,7 @@
         .note-attachment
           - if note.attachment.image?
             = link_to note.attachment.url, target: '_blank' do
-              = image_tag note.attachment.url, class: 'note-image-attach'
+              = image_tag note.attachment.url, class: 'note-image-attach col-lg-4'
           .attachment
             = link_to note.attachment.url, target: '_blank' do
               = sprite_icon('paperclip')