[Flexiglass] Disable NSSL.getScrollAmountToScrollBoundary usages

- Make NSSL.getScrollRange() always returns 0, because NSSL shouldn't
  have a scroll range anymore. Implicitly this was already happening,
  because NSSL.mContentHeight was never set.
- NSSL.clampScrollPosition() was already a no-op, because
  NSSL.setOwnScrollY doesn't do anything.
- NSSL.updateScrollStateForRemovedChild was already a no-op, because we
  cannot animate stackY changes, or contol NSSL.mOwnScrollY.

Bug: 360091533
Test: verify if stack scrolling still works
Flag: com.android.systemui.scene_container
Change-Id: I769d15b02eb3c008f20b6504a07b0150d401bdb6