Remove redundant slashes (#28677)

scss/_mixins.scss

@@ -18,7 +18,7 @@
 @import "mixins/text-emphasis";
 @import "mixins/text-truncate";
 
-// // Components
+// Components
 @import "mixins/alert";
 @import "mixins/buttons";
 @import "mixins/caret";
@@ -29,14 +29,14 @@
 @import "mixins/forms";
 @import "mixins/table-row";
 
-// // Skins
+// Skins
 @import "mixins/background-variant";
 @import "mixins/border-radius";
 @import "mixins/box-shadow";
 @import "mixins/gradients";
 @import "mixins/transition";
 
-// // Layout
+// Layout
 @import "mixins/clearfix";
 @import "mixins/grid-framework";
 @import "mixins/grid";