prune unreachable transitions from HOA and synthesized code

[ravenrothkopf]

Sometimes TSL synthesizes code that contains unreachable transitions. We can prune these to drastically improve code readability for larger specs!

For example, take this generated state written in JavaScript:

if (currentState === 0) {
  if (!x && !y) {
    w = w
    currentState = 1
  }
  else if (!x && y) {
    w = w
    currentState = 1
  }
  else if (!x && y) {
    w = z
    currentState = 1
  }
  else if (x && y) {
    currentState = 2
  }
}

The body of the second else if (!x && y) will never be executed, so we can prune that code. This should be done at the HOA level before code gen.