tests: qemuargv2xmltest: Drop disk for s390 aes tests

tests: qemuargv2xmltest: Drop disk for s390 aes tests

Upcoming patches are going to make the disk portion of these
test cases fail. In order to make it work, we would need to
extend the qemuargv2xml test infrastructure to handle qemuCaps.
This is worthwhile to do at some point but isn't critical.

Instead just drop the offending portion, which isn't even the
target of the test cases anyways