Fix leftover empty 'img' tag from 'random_image' shortcode

layouts/shortcodes/random_image.html

@@ -4,9 +4,7 @@
 {{- end }}
 {{- $alt := default "random image" ($.Page.Param "image.alt") }}
 {{- $id := sha256 (index (seq 999 | shuffle) 0) }}
-<p id="{{ $id }}">
-  <img class="centered pad-vertical" >
-</p>
+<p id="{{ $id }}"></p>
 <script>
 document.addEventListener("DOMContentLoaded", function() {
   const container = document.getElementById("{{ $id }}");