RNA: move the read-only extension "directory" to RNA

This allows it to be exposed in the user interface when the
custom-directory is disabled without having to use a label which can't
handle non UTF-8 characters which file-paths can contain.

scripts/modules/bpy_types.py

@@ -1312,24 +1312,6 @@ class RenderEngine(StructRNA, metaclass=RNAMeta):
     __slots__ = ()
 
 
-class UserExtensionRepo(StructRNA):
-    __slots__ = ()
-
-    @property
-    def directory(self):
-        """Return ``directory`` or a default path derived from the users scripts path."""
-        if self.use_custom_directory:
-            return self.custom_directory
-        import bpy
-        import os
-        # TODO: this should eventually be accessed via `bpy.utils.user_resource('EXTENSIONS')`
-        # which points to the same location (by default).
-        if (path := bpy.utils.resource_path('USER')):
-            return os.path.join(path, "extensions", self.module)
-        # Unlikely this is ever encountered.
-        return ""
-
-
 class HydraRenderEngine(RenderEngine):
     __slots__ = ()