Fix test of wait-for-window-on-boot if wallpaper is disabled

One of condition of the test is to verify that the visible-not-drawn
windows need to wait. But since commit 1e431500, mHasSurface becomes
the criteria of visible window (WindowState#isVisible). So the test
only relied on wallpaper window to pass.

Because config_enableWallpaperService may be false on car product.
That causes the test fails. This change correct the invisible testing
window to restore the original test purpose. So another non-wallpaper
window can take effect to pass the verification.

Bug: 169904362
Bug: 169904497
Test: DisplayContentTests# \
      testShouldWaitForSystemDecorWindowsOnBoot_OnDefaultDisplay
      testShouldWaitForSystemDecorWindowsOnBoot_OnSecondaryDisplay
Change-Id: I5bf3efc82fd600946114b31d921cc5097743393f