Remove deprecated `BackendSampler` from examples

[cqc-melf]

The BackendSampler is deprecated and should be removed from the examples, see:

DeprecationWarning: The class ``qiskit.primitives.backend_sampler.BackendSampler`` is deprecated as of qiskit 1.2. It will be removed no earlier than 3 months after the release date. All implementations of the `BaseSamplerV1` interface have been deprecated in favor of their V2 counterparts. The V2 alternative for the `BackendSampler` class is `BackendSamplerV2`.

[cqc-melf]

Enable the disabled cell from #379 again