Disable backface culling for drawtype plantlike and only draw 2 faces instead of 4

Disable backface culling for drawtype plantlike and only draw 2 faces instead of 4

This way, plants actually show the real backface on their back side,
i.e., the front face mirrored around the vertical axis, instead of
showing the front face on both sides. This looked weird when the
texture was not symmetrical around the vertical axis.