There doesn't seem to be a way of preventing users from creating wiki pages altogether out of the box in my opinion.
However, There are two ways you can achieve your requirement.
- Will work even on the newly created wiki page libraries
- Would require writing code.
Option 2 - By Breaking Permission Inheritance
Go to your Wiki Page Library Settings -> Permissions for this Library
Under Permissions tab on the ribbon, Click on Stop Inheriting Permissions
Click Ok on the dialog box.
Select all the users and groups you want to restrict from creating pages, and click on Edit user permissions in the ribbon.
Assign the users and groups selected Read permissions.
- Completely Out of box and no-code solution, easy to implement
- Only issue with this approach is that you will need to break the permission inheritance of each wiki page library and whenever a new library is created.