Clean up remote driver connection open code

Clean up remote driver connection open code

The remote driver has had a long term hack to deal with the fact
that the old Xen driver worked outside libvirtd, but the rest
of the drivers worked inside. So you could have a local hypervisor
driver but everything else go via the remote driver. The Xen driver
long ago moved inside libvirtd, so this hack is no longer needed.
Thus we should open use the remote driver for secondary drivers
if the primary driver is already the remote driver.