qemu-iotests: remove commented out variables

qemu-iotests: remove commented out variables

The variables FULL_MKFS_OPTIONS and FULL_MOUNT_OPTIONS are commented
out, never used, and even refer to functions that do exist.  The last
time these were touched was around 8 years ago, so I guess it's safe
to assume outputting such information on test execution is still on the
radar.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>