delete method
Deletes and signs out the user.
Important: this is a security-sensitive operation that requires the user to have recently signed in. If this requirement isn't met, ask the user to authenticate again and then call User.reauthenticateWithCredential.
A FirebaseAuthException maybe thrown with the following error code:
Implementation
Future<void> delete() async {
try {
_assertSignedOut(_auth);
await _auth._api.userAccount.delete(_idToken, uid);
await _auth.signOut();
} catch (e) {
rethrow;
}
}