Remove most remaining SCSS extends

Left dropdown-toggle out as I am afraid it will break things
Left table ones as we need some cell/row styles still

app/assets/stylesheets/framework/gfm.scss

@@ -4,7 +4,8 @@
 
 .gfm-commit,
 .gfm-commit_range {
-  @extend .commit-sha;
+  @include gl-font-monospace;
+  font-size: 95%;
 }
 
 .gfm-project_member {

app/assets/stylesheets/pages/search.scss

@@ -45,7 +45,6 @@ input[type='checkbox']:hover {
   margin: 0 8px;
 
   form {
-    @extend .form-control;
     margin: 0;
     padding: 4px;
     width: $search-input-width;
@@ -139,7 +138,6 @@ input[type='checkbox']:hover {
 
   &.search-active {
     form {
-      @extend .form-control:focus;
       border-color: $blue-300;
       box-shadow: none;
 

app/views/layouts/_search.html.haml

 .search.search-form{ data: { track_label: "navbar_search", track_event: "activate_form_input", track_value: "" } }
-  = form_tag search_path, method: :get, class: 'form-inline' do |_f|
+  = form_tag search_path, method: :get, class: 'form-inline form-control' do |_f|
     .search-input-container
       .search-input-wrap
         .dropdown{ data: { url: search_autocomplete_path } }