[CORE] Depricate traditional round-robin schedalgo

The traditional round-robin schedalgo (i.e. vmm_schedalgo_rr) did not
honor the VCPU priorities hence is of less use in real-life.

In Xvisor, all schedalgo's must honor the VCPU priorities for proper
functioning of the hypervisor hence this patch depricates/removes the
traditional round-robin schedalgo.

Signed-off-by: Anup Patel <anup@brainfault.org>