Droppable: Fix bubbling of greedy droppables

[dritter]

• Remove code that made the false assumption that if dragging an element
  out of the greedy child, it is always over the parent. This is not
  always true, as the child could be right on the parents border, or
  even pushed (partially) outside of the parent.

• This commit includes the fixes of maimairel, the original author of
  #9389 from his fiddle http://jsfiddle.net/fvjF4/

This fiddle demonstrates the fix: https://jsfiddle.net/dritter/36gvy1a7/
Just move the blue box over the green boxes. You'll see no yellow flash of the parent box (red).

Fixes: #9389

[jsf-clabot]

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