Fix: Image as planes add-on sets wrong alpha for OpenEXR files

This simply removes the operator property to set the alpha mode, so that
this can be automatically determined. The None case was already handled
by Use Transparency, and Channel Packed doesn't make sense here.

Ref #144009

Pull Request: https://projects.blender.org/blender/blender/pulls/144074

scripts/startup/bl_operators/image_as_planes.py

@@ -367,14 +367,6 @@ class TextureProperties_MixIn:
         description="How the image is extrapolated past its original bounds",
     )
 
-    _Image_alpha_mode = bpy.types.Image.bl_rna.properties["alpha_mode"]
-    alpha_mode: EnumProperty(
-        name=_Image_alpha_mode.name,
-        items=tuple((e.identifier, e.name, e.description) for e in _Image_alpha_mode.enum_items),
-        default=_Image_alpha_mode.default,
-        description=_Image_alpha_mode.description,
-    )
-
     _ImageUser_use_auto_refresh = bpy.types.ImageUser.bl_rna.properties["use_auto_refresh"]
     use_auto_refresh: BoolProperty(
         name=_ImageUser_use_auto_refresh.name,
@@ -400,9 +392,6 @@ class TextureProperties_MixIn:
 
             row = body.row(align=False, heading="Alpha")
             row.prop(self, "use_transparency", text="")
-            sub = row.row(align=True)
-            sub.active = self.use_transparency
-            sub.prop(self, "alpha_mode", text="")
 
             body.prop(self, "use_auto_refresh")
 
@@ -944,8 +933,6 @@ class IMAGE_OT_import_as_mesh_planes(
     def apply_image_options(self, image):
         if not self.use_transparency:
             image.alpha_mode = 'NONE'
-        else:
-            image.alpha_mode = self.alpha_mode
 
         if self.relative:
             try:  # Can't always find the relative path (between drive letters on windows).