Revert "Issue #1356602 by nicholasruunu, mcjim, rteijeiro, chrisjlee | jenlampton: Clean up icons in misc."

This clean-up accidentally introduced a few regressions, so rolling back until it's ready.

This reverts commit fab42693f8.

core/modules/forum/css/forum.module.css

@@ -16,7 +16,7 @@
   white-space: nowrap;
 }
 #forum .icon{
-  background-image: url(../images/forum-icons.png);
+  background-image: url(../../../misc/forum-icons.png);
   background-repeat: no-repeat;
   float: left; /* LTR */
   height: 24px;

core/tests/Drupal/Tests/Core/Image/ImageTest.php

@@ -149,7 +149,7 @@ class ImageTest extends UnitTestCase {
    * Tests \Drupal\Core\Image\Image::setSource().
    */
   public function testSetSource() {
-    $source = __DIR__ . '/../../../../../misc/help.png';
+    $source = __DIR__ . '/../../../../../misc/grippie.png';
     $this->image->setSource($source);
     $this->assertEquals($this->image->getSource(), $source);
   }