Remove opposite position of nav bar for short aspect ratio app

To be consistent as non-resizable activity shown in different display
size that is horizontal centered, the case of fixed aspect ratio also
follows the same letterboxing.

Without removing the opposite position calculation, it will produce
an intermediate bounds that makes seamless rotation flicker.

Supplement:
- The letterboxing test was done in AppWindowTokenTests#testSizeCompatBounds
- Reference of the discussion of original position: b/62893418

Bug: 112288258
Fixes: 124453651
Test: atest ActivityRecordTests
Change-Id: Ie8d492910c48c8425f45f9c61a798854d3908591