Deactivating user from creating new pages is related to your permission setting that assigned to this user, so you have to deactivate "create new page" by assigning on of the following permission level :
- Read. ( Can view pages and list items and download documents.)
- Or Limited access.(Can view specific lists, document libraries, list items, folders, or documents when given permissions.)
- Or View Only. (Can view pages, list items, and documents. Document types with server-side file handlers can be viewed in the browser but not downloaded.)
- Or Restricted Read (Can view pages and documents, but cannot view historical versions or user permissions.)
- Or custom permission level with disallowing create new page with uncheck
Add and Customize Pages - Add, change, or delete HTML pages or Web Part Pages, and edit the Web site using a Microsoft SharePoint
Foundation-compatible editor.
To check the permissions levels , navigate yo http://yourwebroot/_layouts/15/role.aspx