libvirt-guests: Remove obsolete Windows comment
libvirt-guests: Remove obsolete Windows comment

The comment that

> For instance, qemu-ga doesn't support guest time synchronization on
> Windows guests, but Linux ones.

Was correct at the time, but has since been addressed by
qemu/qemu@105fad6bb22, which added support for set-time without a time
argument, as used by `virsh domtime --sync` by libvirt-guests.sh.  I can
confirm that `virsh domtime --sync` works correctly on a Windows 10
guest, as does `SYNC_TIME=1`.  (Note that there can be a significant
delay between when the command completes and when the guest time
finishes synchronizing due to QEMU GA calling `w32tm` with `/nowait`,
which complicates testing.)

Signed-off-by: Kevin Locke <ffb4761cba839470133bee36aeb139f58d7dbaa9@kevinlocke.name>

olafhering/libvirt,crobinso/libvirt,nertpinx/libvirt,libvirt/libvirt,olafhering/libvirt,nertpinx/libvirt,crobinso/libvirt,jfehlig/libvirt,olafhering/libvirt,zippy2/libvirt,olafhering/libvirt,libvirt/libvirt,jfehlig/libvirt,zippy2/libvirt,nertpinx/libvirt,crobinso/libvirt,jfehlig/libvirt,zippy2/libvirt,crobinso/libvirt,libvirt/libvirt,libvirt/libvirt,nertpinx/libvirt,zippy2/libvirt,nertpinx/libvirt,jfehlig/libvirt