Move 0.12 prelude into another note (#1592)

The commit with the 0.12.0 release notes prelude did not make it into
the 0.12.0 tag so reno will treat it as being part of 0.12.1 or 0.13.0.
Here we delete the prelude's note and move its content back into an
earlier note file that did make the 0.12.0 release.

Author: wshanks

releasenotes/notes/add-benchmark-suffix-c3ab8c14c89edb33.yaml

@@ -1,4 +1,9 @@
 ---
+prelude: >
+    Qiskit Experiments 0.12 introduces a new option for labeling results of
+    layer fidelity experiments. Additionally, it addresses an incompatibility
+    with :external+qiskit_ibm_runtime:doc:`qiskit-ibm-runtime <index>` version
+    0.41 that prevents experiments from running.
 features:
   - |
     A new ``benchmark_suffix`` argument for the :class:`~.LayerFidelity`