Pure JS (ES2015) solution, in my opinion easier to read than jQuery-solutions.
node.replaceWith(...node.childNodes)
Node has to be an ElementNode
const wrapperNode = document.querySelector('h1')
wrapperNode.replaceWith(...wrapperNode.childNodes)
<h1>
<a>1</a>
<b>2</b>
<em>3</em>
</h1>