bhyve: Remove unused vm and vcpu arguments from vm_copy routines.

The arguments identifying the VM and vCPU are only needed for
vm_copy_setup.

Reviewed by: corvink, markj
Differential Revision: https://reviews.freebsd.org/D37158

(cherry picked from commit 2b4fe856f44ded02f3450bac1782bb49b60b7dd5)