Removing Crouton and Restoring Your Chromebook
If you decide you’re done with Linux, you can easily get rid of the scary boot screen and get your internal storage space back.
Just reboot your Chromebook normally to get back to the scary warning screen at boot-up. Follow the prompts on your screen (tap the Space bar and then press Enter) to disable Developer Mode. When you disable Developer Mode, your Chromebook will clean everything up, restoring you to a clean, safe locked-down Chrome OS system and overwriting all the changes you’ve made to your Chromebook’s software.
si tu n'as fait aucune de ces actions, tu es toujours en mode dev