Google has removed the public version of their submit URL tool.  This tool allowed anyone to submit a URL to Google, as it wasn’t restricted to site owners only,

Why was this done?  While there were some site owners who used it to submit URLs who were unaware of Google Search Console, it is likely the majority of those using the tool were SEOs to submit pages they didn’t own.  SEOs could submit a URL for a page they have a link on, to get the link indexed and pushing PageRank faster.  Or they could use it to get a social media page indexed faster, often for reputation management purposes, such as a Facebook page or Twitter profile.  Some would do it on competitor sites to get spammy pages indexed and then file a spam report.

They do suggest the alternative ways for site owners to submit their pages via search console, either Fetch and Submit or via sitemaps, something most site owners were doing already.  Their developer documents also suggest Pubsubhubbub for those using Atom/RSS.