Also remove text node in :remove() operator

Related discussion:
- https://github.com/gorhill/uBO-Extra/issues/119#issuecomment-537842967

As an incidental side effect, this may or may not
prevent execution of the content of some inline
script tags.

src/js/contentscript.js

@@ -813,6 +813,7 @@ vAPI.DOMFilterer = (function() {
 
         removeNodes(nodes) {
             for ( const node of nodes ) {
+                node.textContent = '';
                 node.remove();
             }
         }