LMS: removes broken home header image and replaces with basic gradient background

LMS-2121

lms/static/sass/base/_variables.scss

@@ -285,6 +285,13 @@ $footer_margin: ($baseline/4) 0 ($baseline*1.5) 0;
 
 // ====================
 
+// VIEWS: homepage
+$homepage__header--gradient__color--alpha: lighten($blue, 15%);
+$homepage__header--gradient__color--bravo: saturate($blue, 30%);
+$homepage__header--background: lighten($blue, 15%);
+
+// ====================
+
 // IMAGES: backgrounds
 $homepage-bg-image: '../images/homepage-bg.jpg';
 

lms/static/sass/multicourse/_home.scss

@@ -7,8 +7,7 @@
   }
 
   > header {
-    background: $dashboard-profile-color;
-    @include background-image(url($homepage-bg-image));
+    @include linear-gradient($homepage__header--gradient__color--alpha, $homepage__header--gradient__color--bravo);
     background-size: cover;
     border-bottom: 1px solid $border-color-3;
     box-shadow: 0 1px 0 0 $course-header-bg, inset 0 -1px 5px 0 rgba(0,0,0, 0.1);