vm: remove dead (commented out) code
vm: remove dead (commented out) code

default_user property was re-implemented, remove dead version.

QubesOS/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin