vz: remove dependency on `qemu-img` binary for converting qcow2 to raw

[AkihiroSuda]

Maybe we can use https://github.com/dleonard0/read-qcow2 (CC0)

[AkihiroSuda]

Tried to use https://github.com/dleonard0/read-qcow2, but it turned out to fail for most distro images (openSUSE-Leap-15.4-JeOS.x86_64-OpenStack-Cloud.qcow2, CentOS-Stream-GenericCloud-8-20230404.0.x86_64.qcow2, ...) due to ENOTSUP here 😞 :

https://github.com/dleonard0/read-qcow2/blob/189fbe18d2fabdfed20a9a7221460570222dc30b/qcow2.c#L224

[AkihiroSuda]

Wrote by myself https://github.com/lima-vm/go-qcow2reader

[AkihiroSuda]

PR:

• vz: drop dependency on qemu-img #1596