Don't patch IndexObject and Object into git.objects.submodule.util

Such patching, which was introduced in 9519f18, seems no longer to
be necessary. Since git.objects.submodule.util.__all__ has existed
for a long time without including those names, they are not
conceptually public attributes of git.objects.submodule.util, so
they should not be in use by any code outside GitPython either.

The modattrs.py script shows the change, as expected, showing these
two names as no longer being in the git.objects.submodule.util
module dictionary, in output of:

    python modattrs.py >b
    git diff --no-index a b

However, because the removal is intentional, this is okay.

git/objects/__init__.py

@@ -8,17 +8,10 @@
 from .base import *  # noqa: F403
 from .blob import *  # noqa: F403
 from .commit import *  # noqa: F403
-from .submodule import util as smutil
 from .submodule.base import *  # noqa: F403
 from .submodule.root import *  # noqa: F403
 from .tag import *  # noqa: F403
 from .tree import *  # noqa: F403
 
-# Fix import dependency - add IndexObject to the util module, so that it can be imported
-# by the submodule.base.
-smutil.IndexObject = IndexObject  # type: ignore[attr-defined]  # noqa: F405
-smutil.Object = Object  # type: ignore[attr-defined]  # noqa: F405
-del smutil
-
 # Must come after submodule was made available.
 __all__ = [name for name, obj in locals().items() if not (name.startswith("_") or inspect.ismodule(obj))]