account_move.unlink serious performance issue when has lot of lines

If you are deleting an account move with a lot of account move lines, both with code or with client interface, processing time rises exponentially.

Browsing the code, I can see two reasons for this:

- '_update_check' method of 'account_move_line' is called twice. Once in 'unlink' method of 'account_move' and other in 'unlink' method of 'account_move_line'. However this doesn't produce the bottleneck.
- In 'unlink' method of 'account_move', before calling super, 'unlink' method of 'account_move_line' is called, but one optional parameter called 'check' is not present, causing that after every line deleted method 'validate' is called, which slow down a lot the operation.

SOLUTION: I think that calling 'unlink' method of 'account_move_line' with parameter 'check=False' is safe, because you are removing entire account move, and avoid this bottleneck. Also, the '_update_check' call in 'account_move.unlink' can be removed safely.