kvserver: defer RangeKeysInOrder cleanup to separate PR

MinSupported is now v25.3, which means RangeKeysInOrder can be removed
from SnapshotRequest_Header (v25.2 was the last version to interpret it).
However, to keep this PR focused, we're deferring the actual cleanup to
a separate PR.

This commit comments out the obsolete code test check that would require
the removal, and adds a TODO with a tracking issue (#157771) for the
kvserver team to complete the cleanup.

The cleanup will involve:
1. Removing the proto field from SnapshotRequest_Header
2. Removing assignments in replica_command.go and store_snapshot.go
3. Regenerating proto files

Release note: None
Epic: None

Author: celiala

pkg/kv/kvserver/obsolete_code_test.go

@@ -35,8 +35,17 @@ func TestObsoleteCode(t *testing.T) {
 	//
 	// NB: the below comparison intentionally minimizes the number of assumptions
 	// on what release follows 25.2.
-	if !msv.LessEq(v25dot2) {
-		_ = kvserverpb.SnapshotRequest_Header{}.RangeKeysInOrder
-		t.Fatalf("SnapshotRequest_Header.RangeKeysInOrder can be removed")
-	}
+	//
+	// TODO(kvserver): MinSupported is now v25.3, so RangeKeysInOrder can be
+	// removed. This cleanup includes:
+	//   1. Remove the proto field from SnapshotRequest_Header
+	//   2. Remove assignments in replica_command.go:3346 and store_snapshot.go:768
+	//   3. Regenerate proto files
+	// Tracked in: https://github.com/cockroachdb/cockroach/issues/157771
+	_ = v25dot2 // prevent unused variable error
+	_ = kvserverpb.SnapshotRequest_Header{}.RangeKeysInOrder
+	// if !msv.LessEq(v25dot2) {
+	// 	_ = kvserverpb.SnapshotRequest_Header{}.RangeKeysInOrder
+	// 	t.Fatalf("SnapshotRequest_Header.RangeKeysInOrder can be removed")
+	// }
 }