Modified screencap code to use the new captureScreen method that accepts either
the layerStack or displayId. This removes the need to get the displayInfo from
SurfaceFlinger explicitely. The captureScreen function in SurfaceFlinger will
handle getting the correct display information to take the screenshot.
Test: adb shell screencap -d <layerStack for virt display>
Fixes: 130974213
Change-Id: I644bff547bed7d24284b8a6e7899a567d1f4cddf
a69a1b8d70