The current code was doing very slow ops -- effectively O(n^2) lookups for
large histories, to detect no-longer-in-history txns. We instead use
CPython native implementation of the frozenset difference operator to
accomplish the same thing and turn the operation into O(n).

This is a backport of https://github.com/Electron-Cash/Electron-Cash/commit/c2b697a4c0d0d2243ad553f6916d43751c262966

Depends on D14784

Receive a transaction and check if the history list still works.

pytest electrumabc/tests/regtest/