How to delete a wiki page

The answer is, you can't do it. As an ordinary user you can't delete a page. So the procedure is to remove all content from the page and replace it with {{Delete|reason}}. In this case you're removing the #REDIRECT and replace that with {{Delete|created by mistake}}. You can expect a wiki admin to delete the page fully within a few weeks.

The MediaWiki user help has a section on deleting a page written by some very wise chap :-) As explained on that site, there are often better alternatives to deleting, but in this case the page should be deleted. It's clear-cut.

Note that the Delete label template is intended to be used in cases where the delete is clear-cut and should always replace all content of the page. In a case where you feel that a page should be deleted, but you're not confident enough to delete the content yourself (or disputed / potentially deputed deletes), you should use {{delete proposal}} instead (Template:Delete proposal)

The reason a normal user is not allowed to delete a page, is the principle of reversible change. On a busy wikis which must also be vandal-proof, all user changes must be reversible by other users. In actual fact MediaWiki applies this principle to admin users too, so when an admin 'deletes' a page, this change can still be reversed by other admin users. So it turns out we never save any database space by deleting pages. The only benefit is de-cluttering search results.

It's rather harmless to keep it around. To delete it you'd need administrator privileges.

If you add {{delete|reason}} to the page it will be added to Category:Labelled for deletion and eventually an admin should get to it. I don't know if that will happen.