debian: Move creation of directories into debian.dirs configuration file

debian/qubes-core-agent.dirs

@@ -0,0 +1,2 @@
+var/lib/qubes
+lib/modules

debian/qubes-core-agent.preinst

@@ -52,13 +52,6 @@ if [ "$1" = "install" ] ; then
     usermod -p '' root
     usermod -L --groups qubes,sudo user
 
-    # --------------------------------------------------------------------------
-    # Create required directories
-    # --------------------------------------------------------------------------
-    mkdir -p /var/lib/qubes
-    mkdir -p /lib/modules
-    #mkdir -p -m 0700 /var/log/xen  # xen-utils-common should do this
-
     # --------------------------------------------------------------------------
     # Remove `mesg` from root/.profile?
     # --------------------------------------------------------------------------