mvcc: revert change made by 10526
mvcc: revert change made by 10526

Revert #10526 and its followup #10699.

rnaveiras/etcd,cockroachdb/etcd,etcd-io/etcd,coreos/etcd,rnaveiras/etcd,ajityagaty/etcd,etcd-io/etcd,rnaveiras/etcd,li-ang/etcd,dannysauer/etcd,mkumatag/etcd,mkumatag/etcd,mkumatag/etcd,mqliang/etcd,coreos/etcd,ajityagaty/etcd,cockroachdb/etcd,mqliang/etcd,gyuho/etcd,etcd-io/etcd,mqliang/etcd,ajityagaty/etcd,li-ang/etcd,dannysauer/etcd,gyuho/etcd