Revert validation mismatch temp file persistence

This commit reverts 4e469f8 which was used for debugging the validation
stall corruption issue. It can cause the disk to fill with temporary
files though so it is being reverted.

replica.go

@@ -1049,11 +1049,12 @@ func ValidateReplica(ctx context.Context, r Replica) error {
 	if err != nil {
 		return err
 	}
+	defer os.RemoveAll(tmpdir)
 
 	// Compute checksum of primary database under lock. This prevents a
 	// sync from occurring and the database will not be written.
 	primaryPath := filepath.Join(tmpdir, "primary")
-	chksum0, pos, err := db.CRC64(primaryPath)
+	chksum0, pos, err := db.CRC64()
 	if err != nil {
 		return fmt.Errorf("cannot compute checksum: %w", err)
 	}