Let users on email auth delete their mobile numbers

Sometimes users ask us to delete their mobile numbers for them.

If those users are on email auth, they should be able to
delete their number themselves.

This will save them writing a support ticket and save us
going into the database.

app/main/views/user_profile.py

@@ -118,22 +118,43 @@ def user_profile_email_confirm(token):
 
 
 @main.route("/user-profile/mobile-number", methods=['GET', 'POST'])
+@main.route(
+    "/user-profile/mobile-number/delete",
+    methods=['GET'],
+    endpoint="user_profile_confirm_delete_mobile_number"
+)
 @user_is_logged_in
 def user_profile_mobile_number():
 
+    user = User.from_id(current_user.id)
     form = ChangeMobileNumberForm(mobile_number=current_user.mobile_number)
 
     if form.validate_on_submit():
         session[NEW_MOBILE] = form.mobile_number.data
         return redirect(url_for('.user_profile_mobile_number_authenticate'))
 
+    if (request.endpoint == "main.user_profile_confirm_delete_mobile_number"):
+        flash("Are you sure you want to delete your mobile number from Notify?", 'delete')
+
     return render_template(
         'views/user-profile/change.html',
         thing='mobile number',
-        form_field=form.mobile_number
+        form_field=form.mobile_number,
+        user_auth=user.auth_type
     )
 
 
+@main.route("/user-profile/mobile-number/delete", methods=['POST'])
+@user_is_logged_in
+def user_profile_mobile_number_delete():
+    if current_user.auth_type == 'sms_auth':
+        abort(403)
+
+    current_user.update(mobile_number=None)
+
+    return redirect(url_for('.user_profile'))
+
+
 @main.route("/user-profile/mobile-number/authenticate", methods=['GET', 'POST'])
 @user_is_logged_in
 def user_profile_mobile_number_authenticate():