How To Disable WordPress Core Update Notification
It’s very important that you keep your WordPress installation(s) up to date. If you don’t, your blog or website could be susceptible to security vulnerabilities or performance issues. If you use this plugin, you must make sure you keep yourself informed of new WordPress releases and update your WordPress installation(s) as new versions are released.
Disable WordPress Core Update Plugin Completely disables the core update checking system in WordPress. The plugin prevents WordPress from checking for updates, and prevents any notifications from being displayed in the admin area.