Remove image box-shadow in media modal

The box-shadow causes an image to be very blurry on Webkit browsers
(experienced: Konqueror, Safari; heard of: Chrome) when scaled up
if the initial size of the image is much smaller than the actual size
(e.g. when viewing a very long picture).

The shadow is not really obvious anyway.

src/components/media_modal/media_modal.vue

@@ -161,7 +161,6 @@
   max-height: 100%;
   min-width: 0;
   min-height: 0;
-  box-shadow: 0px 5px 15px 0 rgba(0, 0, 0, 0.5);
   image-orientation: from-image; // NOTE: only FF supports this
   animation: 0.1s cubic-bezier(0.7, 0, 1, 0.6) media-fadein;
 }