Revert "FlutterFragment predictive back"

[justinmc]

Reverts #52302, which seems to have broken back gestures for certain Google customers.

At least 2 Google-specific bugs caused by this:
b/354579427
b/355556397

[jiahaog]

Thanks!

[reidbaker]

Are you sure this is the right call? The Original PR handled that predictive back was not working in flutter fragments. It seems to me that this semi broken state is potentially worse than the regressions.

[justinmc]

Predictive back is non-critical feature that is still unreleased on native Android, though, so removing support for it is probably not a big deal. Meanwhile some of those bugs had problems with navigation in general.

I'll keep this open and come back to this next week, but if anyone needs an immediate fix for this, I think it's ok to merge.

[jiahaog]

The internal team needs this to unblock their release with some urgency, so it'll be good to land this / some other fix soon 🙂

[reidbaker]

The internal team needs this to unblock their release with some urgency, so it'll be good to land this / some other fix soon 🙂

OK, I trust yall to make the right decisions here.

[yaakovschectman]

From triage: What is stopping this revert from landing?

[chinmaygarde]

Triage: Justin says we should wait on landing this. But he will be ready to pull the trigger soonish.

[chinmaygarde]

There seems to be some ongoing conversation in the internal threads. Assuming this is still WIP.

[gmackall]

From android triage: Looks like there is still discussion on internal threads, still assuming this is WIP

[justinmc]

Actually I'll go ahead and close this to get it off of triage lists unless something urgent comes up and it's needed.