server/kvm.py: remove legacy KVM support

The server side API for KVM has been unmaintaned for ages, and targets
very old versions of KVM. Instead of carrying code that is not relevant
or may not work at all, clean it up.

People interested in KVM testing should look at the better maintained
'kvm' test in client/tests.

If there's demand for pure server side KVM test support, we can consider
creating server side code using the client virt/kvm libraries.

Signed-off-by: Cleber Rosa <[email protected]>