Use new captureScreen method with displayId or layerStack

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