It turns out that in case the is-tiled-rendering flag is part of the sdr
model, then that's enough for all the places where so far used a flag on
the output device for this purpose, so change the two users of that
method to use SdrModel::isTiledRendering(), and clean up the now unused
one.

Change-Id: Ife6d3d7e093c04b707497d9588942b38bcd8742d