layout: Move edje_get to legacy only
Here's the reasoning:
- We will expose as many edje APIs as possible (and meaningful) through the elm layout class.
- Access to internal objects is usually risky, as it allows apps to bypass EFL in some ways, leading to potentially undefined behaviours.
- If the need arises we can still add a similar API back to EO, later.
Back to #1, it seems that the need for edje_get() was mostly to
call manual sizing functions, or the missing message_send(). I will
make sure these are accessible from the layout itself.