rm responsive-invisibility mixin since it's only used once

inline the one remaining usage into .hidden-print's definition
rm now-empty scss/_utilities-responsive.scss file

[skip sauce]
[skip validator]

scss/_mixins.scss

@@ -28,7 +28,6 @@
 @import "mixins/label";
 @import "mixins/reset-filter";
 @import "mixins/resize";
-@import "mixins/responsive-visibility";
 @import "mixins/screen-reader";
 @import "mixins/size";
 @import "mixins/tab-focus";

scss/_utilities-responsive.scss

@@ -44,6 +44,6 @@
 
 .hidden-print {
   @media print {
-    @include responsive-invisibility(".hidden-print");
+    display: none !important;
   }
 }

scss/mixins/_responsive-visibility.scss

@@ -1,7 +0,0 @@
-// Responsive utilities
-
-@mixin responsive-invisibility($parent) {
-  #{$parent} {
-    display: none !important;
-  }
-}