This article explains how to disable the dialog allowing to choose the page name and layout.
The main sections of this article are mutually exclusive. This means only one section must be applied, depending on admin decision.
Disabling the dialog entirelyEdit
This section explains how to entirely disable the article creation dialog.
The dialog can be disabled in Preferences > Editing by checking "Disable Create Page pop-up".
Disabling layout selectionEdit
The following code disables only layout selection menu without disabling the dialog itself, for example, if it provides useful information.
Making the blank layout defaultEdit
This section must only be applied if the blank layout should be default. If the standard layout should be default, this section should be ignored.
The blank layout can be made default in Preferences > Editing by checking "Use blank page as default for creating a new page".
Edit MediaWiki:Newpagelayout and remove all the content of the page. Note that if that page has no history (you never did any edit on MediaWiki:Newpagelayout), you'll need to do a first edit on that page without actually blanking it, since your edit won't be saved. Once done, you can blank the page safely.
Update: This is no longer working now. The page now must contain anything. If you simply blank the page, the new page layout will pick the default one (located at messaging). If it contains only spaces and newlines it will pick still the default one. Try to put a dot or something the like.