Revert "mark codethink nodes as down"

This reverts commit 2faced5e.

jenkins-home/offline_nodes

@@ -19,15 +19,6 @@ cbxi4pro0-armhf-rb.debian.net
 wbq0-armhf-rb.debian.net
 
 # investigation needed
-codethink9-arm64.debian.net
-codethink10-arm64.debian.net
-codethink11-arm64.debian.net
-codethink12-arm64.debian.net
-codethink13-arm64.debian.net
-codethink14-arm64.debian.net
-codethink15-arm64.debian.net
-codethink16-arm64.debian.net
-
 
 # Down here nodes are automatically added by the maintenance job when they have
 # been failing their health check or maintenance job for too long.