Make subgroup notification indicate it can't be turned off

app/views/participant_mailer/subgroup_notification.html.haml

 %hr
 %footer
   %p
-    = t 'activities.emails.dont_want_mail'
-    %a{href: "https://aardbei.maartenberg.nl/settings"}
-      = t 'activities.emails.open_settings'
+    = t 'activities.emails.cant_turn_off'

app/views/participant_mailer/subgroup_notification.text.erb

 Aardbei
 
 ---
-<%= t 'activities.emails.dont_want_mail' %>
-https://aardbei.maartenberg.nl/settings
+<%= t 'activities.emails.cant_turn_off' %>

config/locales/activities/en.yml

       open_activity: "Open activity"
       open_settings: "Preferences"
       dont_want_mail: "If you no longer want to receive these emails, change your preferences using the following link:"
+      cant_turn_off: "This email cannot be disabled, because it contains important information."
       ending:
         - "Cheers,"
       attendance_reminder:

config/locales/activities/nl.yml

       open_activity: "Activiteit openen"
       open_settings: "Instellingen"
       dont_want_mail: "Als je dit soort mailtjes niet meer wilt ontvangen, kun je dit uitschakelen via de volgende link:"
+      cant_turn_off: "Omdat deze mail belangrijk is kan je hem niet uitzetten."
       ending:
         - "Met griendelijke vroet,"
         - "Met groetelijke doei,"