Use a linear interpolator for screen off, since the reveal effects already...

Use a linear interpolator for screen off, since the reveal effects already interpolate the reveal amount internally.

This was 'doubling up' interpolators causing unwanted timing effects, such as a seeming pause at the beginning.

Fixes: 191149706
Test: screen off begins faster
Change-Id: I92ad0cd5059b84a79069a4d3da37da1f92d03548