Removed some unused code

- removed define USE_AABB_INDIRECT (which switched between old and new AABB implementation)
- removed define SLIC3R_SLA_NEEDS_WINDTREE (relied on igl and was not used anyway)
- new define SLIC3R_HOLE_RAYCASTER (hides currently unused code)
- slight include cleanup
- removed obsolete source file SupportTreeIGL.cpp

src/libslic3r/SLA/SupportPointGenerator.hpp

@@ -7,6 +7,7 @@
 #include <libslic3r/SLA/SupportPoint.hpp>
 #include <libslic3r/SLA/EigenMesh3D.hpp>
 
+#include <libslic3r/BoundingBox.hpp>
 #include <libslic3r/ClipperUtils.hpp>
 #include <libslic3r/Point.hpp>