Remove the now unnecessary "use_draw_order" trait?

[rahulporuri]

This code has existed in chaco since version 3 so i think it is safe for us to finally remove it.

chaco/chaco/plot_component.py

Lines 65 to 77 in 541f3da

	#: Draw layers in **draw_order**? If False, use _do_draw() (for backwards
	#: compatibility).
	use_draw_order = Bool(True)
	def _use_draw_order_changed(self, old, new):
	"""Handler to catch the case when someone is trying to use the
	old-style drawing mechanism, which is now unsupported.
	"""
	if new == False:
	raise RuntimeError(
	"The old-style drawing mechanism is no longer "
	"supported in Chaco."
	)

chaco/chaco/base_plot_container.py

Lines 45 to 47 in e9af395

	#: Deprecated flag to indicate that a component needed to do old-style
	#: drawing. Unused by any recent Chaco component.
	use_draw_order = Bool(True)

chaco/chaco/axis.py

Lines 235 to 236 in e9af395

	if self.use_draw_order and self.component is not None:
	self._layout_as_overlay(*args, **kw)

chaco/chaco/grid.py

Lines 201 to 202 in e9af395

	if self.use_draw_order and self.component is not None:
	self._layout_as_overlay(*args, **kw)