Remove software cursor support
Created by: ascent12
Closes https://github.com/swaywm/wlroots/issues/1363
See https://github.com/swaywm/wlroots/issues/1363#issuecomment-529786169
Hardware cursor support hasn't been added back yet, see: https://github.com/swaywm/wlroots/issues/1363#issuecomment-530752843
I've updated examples/pointer.c to draw its own cursor. I haven't updated examples/multi-pointer.c yet. They are very similar examples, and I wonder if we really need both.