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.

db.go

@@ -1625,7 +1625,7 @@ func restoreWAL(ctx context.Context, r Replica, generation string, index int, db
 // unable to checkpoint during this time.
 //
 // If dst is set, the database file is copied to that location before checksum.
-func (db *DB) CRC64(dst string) (uint64, Pos, error) {
+func (db *DB) CRC64() (uint64, Pos, error) {
 	db.mu.Lock()
 	defer db.mu.Unlock()
 
@@ -1655,16 +1655,7 @@ func (db *DB) CRC64(dst string) (uint64, Pos, error) {
 	}
 	pos.Offset = 0
 
-	// Copy file, if dst specified.
-	checksumPath := db.Path()
-	if dst != "" {
-		if err := copyFile(dst, db.Path()); err != nil {
-			return 0, Pos{}, err
-		}
-		checksumPath = dst
-	}
-
-	chksum, err := checksumFile(checksumPath)
+	chksum, err := checksumFile(db.Path())
 	if err != nil {
 		return 0, pos, err
 	}