[MISC] Remove fast_simplification submodule.

MANIFEST.in

@@ -3,5 +3,4 @@ include LICENSE
 recursive-include genesis/assets *
 recursive-include genesis/ext/pyrender/fonts *
 recursive-include genesis/ext/pyrender/shaders *
-include genesis/ext/VolumeSampling
-include genesis/ext/fast_simplification/*.h
+include genesis/ext/VolumeSampling

genesis/engine/mesh.py

@@ -14,7 +14,7 @@
 import genesis.utils.gltf as gltf_utils
 import genesis.utils.usda as usda_utils
 import genesis.utils.particle as pu
-from genesis.ext import fast_simplification
+import fast_simplification
 from genesis.repr_base import RBC
 
 
@@ -99,7 +99,8 @@ def decimate(self, decimate_face_num, decimate_aggressiveness, convexify):
                     self._mesh.faces,
                     target_count=decimate_face_num,
                     agg=decimate_aggressiveness,
-                    lossless=(decimate_aggressiveness == 0),
+                    # TODO: lossless option support is pending on fast_simplification package.
+                    # lossless=(decimate_aggressiveness == 0),
                 )
             )