Remove "Open in new window" link option

[ellatrix]

This was added in #2204 (issue), #2628 (PR).

It was hidden in WordPress 4.5, see https://make.wordpress.org/core/2016/03/28/the-editor-in-wordpress-4-5/#comment-29560.

Adding the target="_blank" attribute is considered bad practice for post/articles. Unless you're making a web app where this behaviour can be crucial, the use of it should be discouraged so that the user/reader of your site can chose what to do for themselves. I personally hate using sites that add this to their links so you'll stay on their site longer or come back to it. On mobile devices this can be even more frustrating. It breaks the history of a tab.

We shouldn't easily allow hijacking default link behaviour with a simple toggle. Changing default behaviour should be well thought out, and this UI does not encourage that.

Interesting article: https://css-tricks.com/use-target_blank/

Conclusion: when it is a good reason to use target="_blank", it is either not about links in posts/articles on sites (but web apps of some kind) or you're dealing with a really special site where it would be better to filter all links form the post content. There seems to be absolutely no reason to have UI in WordPress for it, and if you really, really, really want to add the attribute, people are free to edit the HTML or install a plugin for it.

Some other interesting links from https://make.wordpress.org/core/2016/03/28/the-editor-in-wordpress-4-5/#comment-29566:

• https://www.smashingmagazine.com/2008/07/should-links-open-in-new-windows/
• https://blog.libux.co/links-should-open-in-the-same-window-447da3ae59ba

[youknowriad]

related #4450

[karmatosed]

I would +1 to remove it.

[braders]

Also related #4499