Google announced Wednesday morning that it turned off public methods of submitting URLs to its search index. The "addurl" page, which is still listed in this help document, is now redirected to the Google Search Console login page.
Google Webmaster said, "We have to cancel the public delivery feature." The company did not say why it was necessary to drop it. It may have something to do with spam or abuse issues. Google added, "... but we continue to receive your submissions using the usual tools in Search Console and through the sitemap directly."
The last time Google updated the post content tool was back in 2012, when it was moved to a classic Google Webmaster Tools URL.
Google says webmasters must submit content only through Search Console's Fetch as a Google tool or through a site map.
Here is a screen shot of the tool working when you are logged in:
Here it is when you try the web search method if you are logged in:
Postscript: A few hours after publishing this story, the public submits the URL form was deleted. Here's how it looks now: