fixing html pt. 1: duplicate DOM element id "langDropdown"

removed the id entirely, not used anywhere in css/scripts
fixing html pt. 2: remove duplicate markdown call

NewsBundle\Entity\NodeNews::getSummary already runs the text through markdown, so don't repeat that
If we wouldn't remove all <p> elements, this would result in invalid html, because
<p><p></p></p> is invalid code:
</p> is optional if the <p> is followed by <div>, <p>, ...
so <p><p></p></p> is the same as <p></p><p></p></p>
which contains a superfluous </p>
Merge branch 'dev-html'