KVM: selftests: Drop @num_percpu_pages from __vm_create_with_vcpus()

Drop @num_percpu_pages from __vm_create_with_vcpus(), all callers pass
'0' and there's unlikely to be a test that allocates just enough memory
that it needs a per-CPU allocation, but not so much that it won't just do
its own memory management.

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