clusterversion,kv: remove ReplicaVersions

Partially addresses cockroachdb#66544 by removing a cluster version and its associated
dependencies which, for any cluster whose version is at least 21.1, is certain
to be active.

Release justification: cluster version cleanup

pkg/clusterversion/cockroach_versions.go

@@ -180,8 +180,6 @@ const (
 	//
 	// Start21_1 demarcates work towards CockroachDB v21.1.
 	Start21_1
-	// ReplicaVersions enables the versioning of Replica state.
-	ReplicaVersions
 	// replacedTruncatedAndRangeAppliedStateMigration stands in for
 	// TruncatedAndRangeAppliedStateMigration which was	re-introduced after the
 	// migration job was introduced. This is necessary because the jobs
@@ -359,10 +357,6 @@ var versionsSingleton = keyedVersions{
 		Key:     Start21_1,
 		Version: roachpb.Version{Major: 20, Minor: 2, Internal: 2},
 	},
-	{
-		Key:     ReplicaVersions,
-		Version: roachpb.Version{Major: 20, Minor: 2, Internal: 12},
-	},
 	{
 		Key:     replacedTruncatedAndRangeAppliedStateMigration,
 		Version: roachpb.Version{Major: 20, Minor: 2, Internal: 14},

pkg/kv/kvserver/store_snapshot.go

@@ -16,7 +16,6 @@ import (
 	"io"
 	"time"
 
-	"github.com/cockroachdb/cockroach/pkg/clusterversion"
 	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/raftentry"
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/rditer"
@@ -924,10 +923,6 @@ func SendEmptySnapshot(
 		return err
 	}
 
-	var replicaVersion roachpb.Version
-	if st.Version.IsActive(ctx, clusterversion.ReplicaVersions) {
-		replicaVersion = st.Version.ActiveVersionOrEmpty(ctx).Version
-	}
 	ms, err = stateloader.WriteInitialReplicaState(
 		ctx,
 		eng,
@@ -936,7 +931,7 @@ func SendEmptySnapshot(
 		roachpb.Lease{},
 		hlc.Timestamp{}, // gcThreshold
 		stateloader.TruncatedStateUnreplicated,
-		replicaVersion,
+		st.Version.ActiveVersionOrEmpty(ctx).Version,
 	)
 	if err != nil {
 		return err