Cycles/Eeeve: unify film transparent setting

For existing files, it will use the setting from Cycles or Eevee depending on
the render engine in the scene.

Differential Revision: https://developer.blender.org/D4874

release/scripts/startup/bl_operators/clip.py

@@ -850,9 +850,6 @@ class CLIP_OT_setup_tracking_scene(Operator):
         # Ensure no nodes were created on the position of existing node.
         self._offsetNodes(tree)
 
-        if hasattr(scene, "cycles"):
-            scene.cycles.film_transparent = True
-
     @staticmethod
     def _createMesh(collection, name, vertices, faces):
         from bpy_extras.io_utils import unpack_list