Observer to strip <p> tags for Magento 2

ElephantData.php

<?php

namespace Elephant\CFParent\Helper;

class ElephantData extends \Magento\Framework\App\Helper\AbstractHelper
{

	public function __construct( 
    	\Magento\Framework\App\Helper\Context $context,
    	array $data = []
    ) {

    	/**
    	 * Data for further use in the widgets is collected here and can be instanced by injecting it in the child widget
    	 * Example: \Elephant\CFParent\Helper\ElephantData $elephantData
    	 **/

        parent::__construct( $context, $data );
    }

    public function processContent($content)
	{
	    // Remove wrapping paragraphs around widgets:
	    $content = preg_replace('/\<p\>{{(.*?)}}\<\/p\>/', '{{$1}}', $content);
	 
	    // Remove div around widgets
	    $content = preg_replace('/\<div\>{{(.*?)}}\<\/div\>/', '{{$1}}', $content);
	 
	    // Remove empty paragraphs:
	    $content = preg_replace('/<p>(|\s*|&nbsp;|\n)<\/p>/', '', $content);
	 
	    return $content;
	}
}

events.xml

<?xml version="1.0" encoding="UTF-8"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../../lib/internal/Magento/Framework/Event/etc/events.xsd">
    <event name="cms_page_render">
        <observer name="elephant_cfparent_controller_cms_page_render" instance="Elephant\CFParent\Model\Observer" />
    </event>
</config>

Observer.php

<?php

namespace Elephant\CFParent\Model;

use Magento\Framework\Event\ObserverInterface;

class Observer implements ObserverInterface {

    /**
     * @param Item $item
     */
    public function __construct(
        \Elephant\CFParent\Helper\ElephantData $elephantData
    ) {
        $this->_elephantData = $elephantData;
    }

    /**
     * @override
     * @see ObserverInterface::execute()
     * @used-by \Magento\Framework\Event\Invoker\InvokerDefault::_callObserverMethod()
     * @see \Magento\Framework\App\Action\Action::dispatch()
     */
    public function execute(\Magento\Framework\Event\Observer $observer) {

        $page       = $observer->getPage();
        $content    = $page->getContent();
        $content    = $this->_elephantData->processContent( $content );

        $page->setContent($content);

    }
}

Giel Berkers forked this and made it compliant with having widgets in blocks too: https://gist.github.com/kanduvisla/d010b36639f79641bb76. If you stumble across this, use that one!