Remove unnecessary constructors from `UMElem`

[WhatisRT]

All elements in the UMap need to have a deposit & reward amount. So the half of the constructors that don't have that should be unused. Also, Conway removes pointer addresses, so there's no reason to keep a set of pointers around, cutting the amount of constructors in half again.

[lehins]

Related ticket: #4693

In order to remove pointers from the DState, we need to turn CertState into a type family