Deleting children block crashes the app

[AlexandreSajus]

Pressing Delete in this configuration crashes the app:

with error:

Traceback (most recent call last):
  File "C:\Users\asaju\Desktop\Pyflow\OpenCodeBlocks\pyflow\graphics\window.py", line 424, in onEditDelete
    current_window.view.deleteSelected()
  File "C:\Users\asaju\Desktop\Pyflow\OpenCodeBlocks\pyflow\graphics\view.py", line 384, in deleteSelected
    selected_item.remove()
  File "C:\Users\asaju\Desktop\Pyflow\OpenCodeBlocks\pyflow\blocks\block.py", line 176, in remove
    socket.remove()
  File "C:\Users\asaju\Desktop\Pyflow\OpenCodeBlocks\pyflow\core\socket.py", line 113, in remove
    self.block.sockets_in.remove(self)
ValueError: list.remove(x): x not in list