Remove unused sass resources in css folder and simplify them

Author: calvinl

common/css/_functions.scss

@@ -0,0 +1 @@
+/* Import or define any sass mixins and functions below */

common/css/_variables.scss

@@ -0,0 +1 @@
+// Variables, like colors and widths/heights here.

common/css/_vendors.scss

@@ -0,0 +1,3 @@
+/* Import or define any sass mixins, functions, and vendor mixins below */
+
+@import "~include-media/dist/include-media";