Multisample buffers were used for smooth line drawing. As we now have
an algorithm that doesn't need the multisample buffers we can remove
them.
The user preference for viewport multi_sampling is replaced by single
toggle overlay `use_overlay_smooth_wire`. By default this setting is
enabled as the new drawing is really quick (<1ms) and uses zero hacks.
Reviewed By: fclem
Differential Revision: https://developer.blender.org/D6367
15abc9fe74