virtiofs: get rid of no_mount_options

virtiofs: get rid of no_mount_options

This option was introduced so that for virtio_fs we don't show any mounts
options fuse_show_options(). Because we don't offer any of these options
to be controlled by mounter.

Very soon we are planning to introduce option "dax" which mounter should
be able to specify. And no_mount_options does not work anymore.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>