sched/eevdf: Remove min_vruntime_copy

Since commit e8f331bc ("sched/smp: Use lag to simplify
cross-runqueue placement") the min_vruntime_copy is no longer used.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lkml.kernel.org/r/20240727105028.395297941@infradead.org