Remove empty internal qiskit.providers.fake_provider.utils (#15091)

This is an undocumented internal module, so not subject to the
deprecation policy.  The module has been empty since gh-13793 (and the
handful of other `qiskit.providers` PRs that logically went with that
one) in the Qiskit 2.0 transition, but since everything was using
precise imports, we didn't notice the `__init__` file was now useless.

Author: jakelishman