Remove newsletter config - follow up to #1 (#450)

Author: brusch

.github/ci/files/config/system.yml

@@ -63,12 +63,3 @@ pimcore_admin:
         color_login_screen: ''
         color_admin_interface: ''
         login_screen_custom_image: ''
-pimcore_newsletter:
-    sender:
-        name: ''
-        email: ''
-    return:
-        name: ''
-        email: ''
-    debug: null
-    use_specific: true