Delete dead code function SpotShadow::makeClockwise

Delete SpotShadow::makeClockwise, which is unused and does
not link when compiler optimizations are disabled (for debugging).
SpotShadow::makeClockwise calls non-existent function
ShadowTessellator::isClockwise, which only works because the
optimizer deletes the function.

Change-Id: Ib8a014bf168782772faa1da7d75a079c1fd28ed9