devise: unify password reset views

By default, Devise will look for views:

1. First in `views/resource/passwords/…`,
2. Then in `views/devise/passwords/…` if not found.

By moving the views to `views/devise`, we avoid having a partial in
`views/shared` that we need to include manually, and instead let Devise
do the job automatically.

app/controllers/administrateurs/passwords_controller.rb

@@ -1,14 +0,0 @@
-class Administrateurs::PasswordsController < ApplicationController
-  def test_strength
-    @score, @words, @length = ZxcvbnService.new(password_params[:password]).complexity
-    @min_length = PASSWORD_MIN_LENGTH
-    @min_complexity = PASSWORD_COMPLEXITY_FOR_ADMIN
-    render 'shared/password/test_strength'
-  end
-
-  private
-
-  def password_params
-    params.require(:administrateur).permit(:password)
-  end
-end