Xen: xenconfig: remove disks from '(image)' sexpr

It has been quite some time since xend required specifying cdroms
and fds in '(image (hvm ...))'. Remove the code from the parsing
and formatting functions and fixup the associated tests.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>

tests/xml2sexprdata/xml2sexpr-fv-sound.sexpr

@@ -2,7 +2,7 @@
 (uuid 'b5d70dd2-75cd-aca5-1776-9660b059d8bc')(on_poweroff 'destroy')\
 (on_reboot 'restart')(on_crash 'restart')\
 (image (hvm (kernel '/usr/lib/xen/boot/hvmloader')(vcpus 1)(boot c)\
-(cdrom '/root/boot.iso')(acpi 1)(usb 1)(parallel none)(serial none)\
+(acpi 1)(usb 1)(parallel none)(serial none)\
 (soundhw 'sb16,es1370')(device_model '/usr/lib64/xen/bin/qemu-dm')(vnc 1)))\
 (localtime 0)\
 (device (vbd (dev 'ioemu:hda')(uname 'file:/root/foo.img')(mode 'w')))\