evas: Move evas_canvas.eo to legacy-only
This isn't meant to be installed. The canvas API in EO is based around
the interfaces Efl.Canvas and the widget Efl.Ui.Win. Anything else is
not EO (eg: ecore_evas, evas, ...)
Note: evas_canvas3d is the last remaining thing that is installed along
EO files, but those are all beta APIs.