interperter: Remove unused Interpreter.subproject_directory_name

mesonbuild/interpreter/interpreter.py

@@ -281,9 +281,6 @@ class Interpreter(InterpreterBase, HoldableObject):
         self.backend = backend
         self.summary: T.Dict[str, 'Summary'] = {}
         self.modules: T.Dict[str, NewExtensionModule] = {}
-        # Subproject directory is usually the name of the subproject, but can
-        # be different for dependencies provided by wrap files.
-        self.subproject_directory_name = subdir.split(os.path.sep)[-1]
         self.subproject_dir = subproject_dir
         self.relaxations = relaxations or set()
         if ast is None: