We don't need DERSIG forgivness (STRICTENC implies it anyway
so DERSIG violations do get banned) nor CHECKDATASIG_SIGOPS
(irrelevant to CheckInputs) in there. Remove them just as a
quick cleanup.
TODO in future diffs: make SIGPUSHONLY / CLEANSTACK / CLTV / CSV mandatory too
(requires tests).
Depends on D5222