[Dual Shade] Remove the redundant coercion of the shade expand fraction.

The `expandFraction` should be in [0..1] per its API contract, so the
caller shouldn't have to coerce the value.

Bug: 400530515
Test: Unit tests still pass.
Flag: com.android.systemui.scene_container
Change-Id: I3ed890ee4f16ca7fda2cc65d1cd0c542445bbade