Revert "Option required flag"

[kaos]

Reverts #18780.

As discussed in #18792 a less invasive approach is to indicate an options requiredness at runtime when looking up the value rather than as a static declaration enforced at parse time.

[benjyw]

To clarify my comment on #18792 , I think a static option enforced at parse time is fine, just that we shouldn't enforce it at _get_underlying_value lookup time, because that is very invasive. Instead we can do it as an extra step at parse time.

[kaos]

To clarify my comment on #18792 , I think a static option enforced at parse time is fine, just that we shouldn't enforce it at _get_underlying_value lookup time, because that is very invasive. Instead we can do it as an extra step at parse time.

The problem with that is that if you have some required options on a GoalSubsystem that are "ad-hoc" in nature (e.g. they only make sense to provide as CLI flags along with running the goal, as with pants paths --from=.. --to=..) we don't want to err if they're missing when you are not running said goal.

[kaos]

Still, I think it's preferable to back this out and redo it, so we can cut a clean 2.17 dev release.