Simplify CMakeLists.txt for Irrlicht demos.
Simplify CMakeLists.txt for Irrlicht demos.

projectchrono/chrono,armanpazouki/chrono,hsu/chrono,amelmquist/chrono,dariomangoni/chrono,hsu/chrono,dariomangoni/chrono,scpeters/chrono,rserban/chrono,PedroTrujilloV/chrono,scpeters/chrono,andrewseidl/chrono,scpeters/chrono,Bryan-Peterson/chrono,rserban/chrono,armanpazouki/chrono,Bryan-Peterson/chrono,Bryan-Peterson/chrono,Milad-Rakhsha/chrono,andrewseidl/chrono,rserban/chrono,amelmquist/chrono,PedroTrujilloV/chrono,hsu/chrono,jcmadsen/chrono,hsu/chrono,projectchrono/chrono,hsu/chrono,andrewseidl/chrono,dariomangoni/chrono,PedroTrujilloV/chrono,rserban/chrono,PedroTrujilloV/chrono,dariomangoni/chrono,projectchrono/chrono,PedroTrujilloV/chrono,jcmadsen/chrono,projectchrono/chrono,tjolsen/chrono,armanpazouki/chrono,jcmadsen/chrono,andrewseidl/chrono,jcmadsen/chrono,rserban/chrono,tjolsen/chrono,tjolsen/chrono,amelmquist/chrono,Milad-Rakhsha/chrono,Bryan-Peterson/chrono,Milad-Rakhsha/chrono,scpeters/chrono,jcmadsen/chrono,jcmadsen/chrono,Bryan-Peterson/chrono,Milad-Rakhsha/chrono,dariomangoni/chrono,rserban/chrono,scpeters/chrono,amelmquist/chrono,amelmquist/chrono,dariomangoni/chrono,andrewseidl/chrono,projectchrono/chrono,armanpazouki/chrono,rserban/chrono,Milad-Rakhsha/chrono,armanpazouki/chrono,tjolsen/chrono,jcmadsen/chrono,armanpazouki/chrono,tjolsen/chrono,amelmquist/chrono,Milad-Rakhsha/chrono,projectchrono/chrono