MDL-50690 themes: fix commenting coding style

(See also CONTRIB-5891)

theme/image.php

@@ -168,8 +168,8 @@ if (!$usesvg) {
             send_uncached_image($imagefile);
             exit;
         } else {
-            /* We cannot serve the SVG file this time and there is no alternative, so prevent future
-               requests from failing to find the image when they can support SVG. */
+            // We cannot serve the SVG file this time and there is no alternative, so prevent future
+            // requests from failing to find the image when they can support SVG.
             image_not_found();
         }
     }