Brad Angelcyk

This plugin provides an option to disable notification emails send to the admin for both new user and changed/lost passwords.

Disable Email Notifications

Provides an option to disable notifications sent to the site admin.

Sakthivel S

This plugin is used disable the wordpress functionality of updating core, themes & plugins automatically. Also it will disable all kind of update notification from wordpress.org theme/plugin repository.
Features 
* Disable WordPress core, themes, plugin update 
* Disable notifications for all updates available.

Disable All Updates & Notifications

Disable Wordpress, Themes & Plugins Updates along with their update notifications.

Disable Email Notifications vs Disable All Updates & Notifications