Don't accept a second argument to `sendrawtransaction` and
`testmempoolaccept` of type `bool`. Actually even the code before this
change would not accept `bool`, but it would print a long explanatory
message when rejecting it: "Second argument must be numeric (maxfeerate)
and no longer supports a boolean. To allow a transaction with high fees,
set maxfeerate to 0."
This was scheduled for removal in rABC1d4e5281a755
This is a backport of Core PR18495