* Update deprecation policy document for Qiskit 1.0
This updates `DEPRECATION.md` to bring it inline with the documentation
hosted on https://docs.quantum.ibm.com. The policy described in this
commit is intended to match what we already agreed on and posted
publicly, but this particular file got slightly out-of-sync during the
initial deployment of the new hosted documentation and the split of
certain documentation content from this repository.
Most notably, this commit makes the exact extent of the public interface
much clearer. We no longer use the "implicit based on object name"
form, but only commit to publicly documented objects being part of the
public interface.
* Commit to raising a warning on experimental features
* Remove comment on internal import policy
Eric Arellano