Fix link/origin referrer and login redirect (#36279)

Fix #35998

1. Fix `<a rel>` :
    * "_blank" already means "noopener"
* "noreferrer" is already provided by page's `<meta name="referrer">`
2. Fix "redirect_to" mechisam
* Use "referer" header to determine the redirect link for a successful
login
3. Simplify code and merge duplicate logic

modules/markup/html_link.go

@@ -208,7 +208,6 @@ func createDescriptionLink(href, content string) *html.Node {
 		Attr: []html.Attribute{
 			{Key: "href", Val: href},
 			{Key: "target", Val: "_blank"},
-			{Key: "rel", Val: "noopener noreferrer"},
 		},
 	}
 	textNode.Parent = linkNode