Remove unused functions

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mobilizon/users/user.ex

@@ -188,13 +188,6 @@ defmodule Mobilizon.Users.User do
     |> hash_password()
   end
 
-  @doc """
-  Checks whether an user is confirmed.
-  """
-  @spec is_confirmed(t) :: boolean
-  def is_confirmed(%__MODULE__{confirmed_at: nil}), do: false
-  def is_confirmed(%__MODULE__{}), do: true
-
   @doc """
   Returns whether an user owns an actor.
   """