To uninstall Todoist for Gmail:
1. Click the Chrome menu on the browser toolbar.
2. Click Tools and select Extensions.
3. Click the trash can icon by the extension you'd like to completely remove.
4. A confirmation dialog appears, click Remove.
You can also temporarily turn off an extension by disabling it on the Extensions page.
I successfully uninstalled 'todolist' from my desktop.
However, this morining I received a 'digest' email.
How to I prevent emails and deny 'todolist' access to my calendar/emails
Head into Todoist Settings (website, top right gear icon) and turn them off from there. You could also in the same settings go to Account and delete your account.