KVM: selftests: Use vCPU's CPUID directly in Hyper-V test

Use the vCPU's persistent CPUID array directly when manipulating the set
of exposed Hyper-V CPUID features.  Drop set_cpuid() to route all future
modification through the vCPU helpers; the Hyper-V features test was the
last user.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-27-seanjc@google.com