Eliminate boolean properties

[WhatisRT]

For convenience or other reasons, some properties/predicates produce booleans. Our properties should always go to Set, so we can use them without writing something like ≡ true.

Here are some offenders:

• [x] actionWellFormed
• [ ] isP2Script
• [ ] isAdaOnlyᵇ
• [ ] feesOK

delayingAction is an exception, since we use this to update an actual Bool in a state.