Drop unused compat assets volume

start-sdk pack was failing on 'Copying Assets: No such file'
because the compat volume was declared with type: assets but
had no assets/compat/ directory to populate it.

manifest.yaml

@@ -40,7 +40,6 @@ main:
   mounts:
     main: /root/.kamado
     ckpool: /root/.ckpool
-    compat: /mnt/assets
   gpu-acceleration: false
 
 hardware-requirements:
@@ -68,8 +67,6 @@ volumes:
     type: data
   ckpool:
     type: data
-  compat:
-    type: assets
 
 interfaces:
   main: