Abandoned pauses in G1 are ones for which we end up having an empty collection set. So, we deem there's no point in actually doing the pause and we bail out early.

As part of "6944166: G1: explicit GCs are not always handled correctly" we are disabling abandoned pauses, i.e., we assume a pause is never abandoned even if the collection set is empty (see that CR for the reasons for this).

As part of this CR we'll remove the code paths that are associated with abandoned pauses. This work is done separately to avoid adding more changes to 6944166 and keep the code reviews somewhat more managable.