MNT : fix `__init__` order in AnchoredSizeLocator

Trying to set the axes property before calling up the mro to the base
class (eventually Artist) `__init__` which means that the `_axes`
attribute is not yet attached to the instance object.

 - removed setting of `self.axes`, this is taken care of in the
   baseclass
 - moved rest of sub-class specific attributes to after call up mro
   stack