Remove altOrientation from DisplayContent.

altOrientation was used for pillarbox/letterbox when display can't
accommodate app's orientation request to limit display bounds to a
pillarbox/letterbox. This feature has been completely replaced by the
new letterbox mechanism implmented at task level, so we can remove it
now.

Bug: 113252523
Test: Builds, go/wm-smoke and atest DisplayContentTests
Change-Id: I59924f7b5f1f7558d9f848222e4613ab73dd89bf