tests: remove explicit <driver name='vfio'/> from hostdev test cases

tests: remove explicit <driver name='vfio'/> from hostdev test cases

The long-deprecated use of <driver name='vfio|xen|kvm'/> in domain xml
for <hostdev> devices was only ever necessary during the period when
libvirt (and the Linux kernel) supported both VFIO and "legacy KVM"
styles of hostdev device assignment for QEMU. This became pointless
many years ago when legacy KVM device assignment was removed from the
kernel, and support for that style of device assignment was completely
disabled in the libvirt source in 2019 (commit
v5.6.0-316-g2e7225ea8c).

Nevertheless, there were instances of <driver name='vfio'/> in the
unit test data that were then (unnecessarily) propagated to several
more tests over the years. This patch cleans out those unnecessary
explicit settings of driver name='vfio' in all QEMU unit test data,
proving that the attribute is no longer (externally) needed. (A later
patch which adds a 2nd attribute to the <driver> element will include
a test case that explicitly exercises the driver name attribute).

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>