Sun position: remove default texture name from Sky Texture

This prevents the add-on taking over the rotation of the sky texture,
as reported in T78618 and many other bug reports.

sun_position/properties.py

@@ -162,7 +162,7 @@ class SunPosProperties(PropertyGroup):
 
     sky_texture: StringProperty(
         name="Sky Texture",
-        default="Sky Texture",
+        default="",
         description="Name of sky texture to be used",
         update=sun_update)