Improve cross platform support in QEMU machine sources

[arixmkii]

Bugfixes extracted from a bigger change #21594

This change:

• cleanups some old Windows bits used in machine 4 times;
• converts socket path into cross platform compatible in gvproxy command
• fixes typo in log
• resolves QEMU settings from machine config QEMUHypervisor part instead of QEMUStubber. In my testing it was always resulting in {nil} QMP socket and incorrect machine termination on Windows. I haven't yet checked it on Linux.

Does this PR introduce a user-facing change?

None

[NO NEW TESTS NEEDED]

[packit-as-a-service]

Ephemeral COPR build failed. @containers/packit-build please check.

[arixmkii]

I also checked stubbers for all other providers. If one completely removes vmconfig from there everything seems to compile. It looks like this vmconfig part of Stubber is a sort of work in progress, which was only referenced in QEMU machine, where the real machine config is also available. This part is really weird.

[rhatdan]

Thanks @arixmkii
LGTM
@ashley-cui @baude @jakecorrenti PTAL

[baude]

good catch

LGTM

/approve

[openshift-ci]

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[rhatdan]

/lgtm