CT-1736 remove apt-get source "nodesource"
CT-1736 remove apt-get source "nodesource"

The Ruby 2.3 image we use upgraded to Debian stretch which has node built-in so
this is no longer needed.

ministryofjustice/correspondence_tool_staff,ministryofjustice/correspondence_tool_staff,ministryofjustice/correspondence_tool_staff,ministryofjustice/correspondence_tool_staff,ministryofjustice/correspondence_tool_staff