KVM: selftests: Drop @vcpuids param from VM creators

Drop the @vcpuids parameter from VM creators now that there are no users.
Allowing tests to specify IDs was a gigantic mistake as it resulted in
tests with arbitrary and ultimately meaningless IDs that differed only
because the author used test X intead of test Y as the source for
copy+paste (the de facto standard way to create a KVM selftest).

Except for literally two tests, x86's set_boot_cpu_id and s390's resets,
tests do not and should not care about the vCPU ID.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>