Make resolve discussion icon gray

app/assets/stylesheets/pages/notes.scss

@@ -727,6 +727,12 @@ ul.notes {
     border-bottom-left-radius: 0;
   }
 
+  .btn {
+    svg path {
+      fill: $gray-darkest;
+    }
+  }
+
   .btn.discussion-create-issue-btn {
     margin-left: -4px;
     border-radius: 0;
@@ -741,10 +747,6 @@ ul.notes {
         border: 0;
       }
     }
-
-    .new-issue-for-discussion path {
-      fill: $gray-darkest;
-    }
   }
 }
 
@@ -817,16 +819,6 @@ ul.notes {
   vertical-align: middle;
 }
 
-.discussion-next-btn {
-  svg {
-    margin: 0;
-
-    path {
-      fill: $gray-darkest;
-    }
-  }
-}
-
 // Merge request notes in diffs
 .diff-file {
   // Diff is inline