Since virMigratePrepareTunnel() is used for migration over the
native libvirt connection, there is never any need to pass the
target URI to this method.

* daemon/remote.c, src/driver.h, src/libvirt.c, src/libvirt_internal.h,
  src/qemu/qemu_driver.c, src/remote/remote_driver.c,
  src/remote/remote_protocol.c, src/remote/remote_protocol.h,
  src/remote/remote_protocol.x: Remove 'uri_in' parameter from
  virMigratePrepareTunnel() method