ironic-lib uses the deprecated declare_namespace call

[Dmitry Tantsur]

Warning from sushy-tools, for example:

/home/dtantsur/Projects/sushy-tools/.tox/venv/lib/python3.12/site-packages/ironic_lib/__init__.py:18: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
  import pkg_resources
/home/dtantsur/Projects/sushy-tools/.tox/venv/lib/python3.12/site-packages/ironic_lib/__init__.py:19: DeprecationWarning: Deprecated call to `pkg_resources.declare_namespace('ironic_lib')`.
Implementing implicit namespace packages (as specified in PEP 420) is preferred to `pkg_resources.declare_namespace`. See https://setuptools.pypa.io/en/latest/references/keywords.html#keyword-namespace-packages
  pkg_resources.declare_namespace(__name__)

I have no idea why we do this: ironic-lib is not a namespace, just a normal package. This code has been there since the inception. I suspect we can remove it.