styles: Remove unused vertical-align mixin

Author: Turbo87

app/styles/_helpers.scss

@@ -8,11 +8,3 @@
     background: -ms-linear-gradient(top, $start 0%,$end 100%);
     background: linear-gradient(to bottom, $start 0%,$end 100%);
 }
-
-@mixin vertical-align {
-    position: relative;
-    top: 50%;
-    -webkit-transform: translateY(-50%);
-    -ms-transform: translateY(-50%);
-    transform: translateY(-50%);
-}