bpo-42403: Fix pyflakes warnings in importlib (GH-23396)

Remove unused imports and unused local variables.

Lib/importlib/abc.py

@@ -1,5 +1,4 @@
 """Abstract base classes related to import."""
-from . import _bootstrap
 from . import _bootstrap_external
 from . import machinery
 try:

Lib/importlib/machinery.py

@@ -1,7 +1,5 @@
 """The machinery of importlib: finders, loaders, hooks, etc."""
 
-import _imp
-
 from ._bootstrap import ModuleSpec
 from ._bootstrap import BuiltinImporter
 from ._bootstrap import FrozenImporter

Lib/importlib/util.py

@@ -232,7 +232,6 @@ class _LazyModule(types.ModuleType):
         # Figure out exactly what attributes were mutated between the creation
         # of the module and now.
         attrs_then = self.__spec__.loader_state['__dict__']
-        original_type = self.__spec__.loader_state['__class__']
         attrs_now = self.__dict__
         attrs_updated = {}
         for key, value in attrs_now.items():