[Materials] Consider removing Blender 2.79 (and older) references

[pedropaulosuzuki]

Blender 2.80 came out in 30/07/2019, more than 5 years ago. I think it's safe to remove instructions on older versions by now. Maybe we can leave a note/paragraph, but a full section is a bit much.

[qwertychouskie]

I believe not all the tracks have been converted to the new format yet. We should probably convert at least all the core tracks before removing documentation, but honestly I see little good reason to remove documation that's potentially needed for years and years worth of tracks.