Remove the remains of ImmediateGeometry3D

ImmediateGeometry3D was recently removed in favor of the ImmediateMesh
resource.

editor/icons/ImmediateGeometry3D.svg

@@ -1 +0,0 @@
-<svg height="16" viewBox="0 0 16 16" width="16" xmlns="http://www.w3.org/2000/svg"><path d="m2.9208 1046.4c-.26373.3-.4204.7296-.4204 1.2383 0 1.6277-3.1381-.1781-.33757 2.6703.88382.899 2.6544.6701 3.5382-.2288.88384-.899.88382-2.3565 0-3.2554-1.1002-1.1191-2.2001-1.0845-2.7803-.4244zm2.3802-1.6103 2.4005 2.4416 6.8014-6.9177c.66286-.6742.66286-1.7673 0-2.4415-.66288-.6741-1.7376-.6741-2.4005 0z" fill="#fc7f7f" transform="translate(0 -1036.4)"/></svg>

scene/register_scene_types.cpp

@@ -908,7 +908,6 @@ void register_scene_types() {
 	ClassDB::add_compatibility_class("Generic6DOFJoint", "Generic6DOFJoint3D");
 	ClassDB::add_compatibility_class("HeightMapShape", "HeightMapShape3D");
 	ClassDB::add_compatibility_class("HingeJoint", "HingeJoint3D");
-	ClassDB::add_compatibility_class("ImmediateGeometry", "ImmediateGeometry3D");
 	ClassDB::add_compatibility_class("Joint", "Joint3D");
 	ClassDB::add_compatibility_class("KinematicBody", "CharacterBody3D");
 	ClassDB::add_compatibility_class("KinematicBody2D", "CharacterBody2D");