tests: qemuxmlconf: virtiofs: remove locking from the readonly test case

tests: qemuxmlconf: virtiofs: remove locking from the readonly test case

The combination of locking + readonly is bogus, because there has never
been a virtiofsd release that supported both.

Locking was a feature of the C-based virtiofsd that was living in the
QEMU tree until v8.0.0 and the readonly feature was only introduced
in the Rust version of virtiofsd.

Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Laine Stump <laine@redhat.com>