Removed the <time> tag for Unix timestamp in views rest export

Closes #3418845

core/modules/system/templates/time.html.twig

@@ -19,4 +19,10 @@
  * @see https://www.w3.org/TR/html5-author/the-time-element.html#attr-time-datetime
  */
 #}
+
+{% if text matches '/^\\d+$/' %}
+{{ text }}
+{% else %}
 <time{{ attributes }}>{{ text }}</time>
+{% endif %}
+