KVM: selftests: Drop manual CR4.OSXSAVE enabling from CR4/CPUID sync test

Now that CR4.OSXSAVE is enabled by default, drop the manual enabling from
CR4/CPUID sync test and instead assert that CR4.OSXSAVE is enabled.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20241003234337.273364-8-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>