feat(authentication): add method `deleteUser`

[robingenz]

Is your feature request related to a problem? Please describe:

Currently there is no way to delete the user's profile.

Describe the solution you'd like:

Add method deleteUser.

Describe alternatives you've considered:

Additional context:

https://firebase.google.com/docs/auth/web/manage-users#delete_a_user

[trancee]

relates to #260

[robingenz]

@trancee Thanks! :D

Closed as duplicate of #260