After D5221, MANDATORY_SCRIPT_VERIFY_FLAGS is only
used for calculating STANDARD_NOT_MANDATORY_VERIFY_FLAGS,
nothing else. And really the important flag set we care
about for banning is STANDARD_NOT_MANDATORY_VERIFY_FLAGS,
that describes the set of flags which must be removed from
GetStandardScriptFlags in order to determine whether to ban
a peer or not. It's also only indirectly related to
STANDARD_SCRIPT_VERIFY_FLAGS so it doesn't really make
sense to base it on that either.
Note that this exposes exactly what flags we have forgotten
to make mandatory, such as SCRIPT_VERIFY_DERSIG which has
been a consensus rule since ages now. It's not a big deal
since STRICTENC basically includes DERSIG, but still it's
a bit weird that it was missing.
There is no change in the value of these flags here,
they are STANDARD_NOT_MANDATORY_VERIFY_FLAGS == 0x5407A4
both before and after.
Depends on D5221