remove unused file 'vm-cgconfig.conf' (#5127)

Honestly no clue why it's still here, should have been removed ages ago.
This is handled by vm-builder now.

vm-cgconfig.conf

@@ -1,12 +0,0 @@
-# Configuration for cgroups in VM compute nodes
-group neon-postgres {
-    perm {
-        admin {
-            uid = vm-informant;
-        }
-        task {
-            gid = users;
-        }
-    }
-    memory {}
-}