Remove CurveProperties#pageParentScale

Test: Set TaskView#EDGE_SCALE_DOWN_FACTOR = 0.2f, then swipe
down on the centermost TaskView; ensure it fills the screen.
Alternatively, touch and hold the nav bar and ensure there is
no jump in scale on the app window.

Fixes: 169259407
Change-Id: Ib3cfba6ebafbcb90de9c6b1ab79f53605d995321
Merged-In: Ib3cfba6ebafbcb90de9c6b1ab79f53605d995321