Remove docs for <portal>

files/en-us/web/html/element/index.md

@@ -137,7 +137,6 @@ In addition to regular multimedia content, HTML can include a variety of other c
 | {{HTMLElement("iframe")}}      | Represents a nested browsing context, embedding another HTML page into the current one.                                                                                                                                                                                                                                                                                                                                                                                                     |
 | {{HTMLElement("object")}}      | Represents an external resource, which can be treated as an image, a nested browsing context, or a resource to be handled by a plugin.                                                                                                                                                                                                                                                                                                                                                      |
 | {{HTMLElement("picture")}}     | Contains zero or more {{HTMLElement("source")}} elements and one {{HTMLElement("img")}} element to offer alternative versions of an image for different display/device scenarios.                                                                                                                                                                                                                                                                                                           |
-| {{HTMLElement("portal")}}      | Enables the embedding of another HTML page into the current one to enable smoother navigation into new pages.                                                                                                                                                                                                                                                                                                                                                                               |
 | {{HTMLElement("source")}}      | Specifies multiple media resources for the picture, the audio element, or the video element. It is a void element, meaning that it has no content and does not have a closing tag. It is commonly used to offer the same media content in multiple file formats in order to provide compatibility with a broad range of browsers given their differing support for [image file formats](/en-US/docs/Web/Media/Formats/Image_types) and [media file formats](/en-US/docs/Web/Media/Formats). |
 
 ## SVG and MathML