Remove Deprecated Terms

[parsonsmatt]

The DeleteCascade stuff was deprecated with 2.13, along with mpsGeneric. See #1204 for the RFC around fully removing that.

As of this date, Stackage nightly is still on persistent-2.11: commercialhaskell/stackage#5968

I'd like to wait until persistent-2.13 has been in an LTS release before deleting. Tentatively setting to the 2.14 milestone, but will review this when the time comes.

[parsonsmatt]

Stackage LTS 18.0 is using persistent-2.13, so we can remove these terms with a 2.14 release.

[parsonsmatt]

ok so mpsGeneric is something i haven't figured out yet, gonna punt that to 2.15 i guess