Remove the window whose client process has died or become zombie

Window Manager Service would fail to report window-resized to the
process which has become zombie. This would cause the window to
freeze screen continuously. In this case, we assume the process has
died and remove its window to recycle resources and to prevent it from
freezing the screen.

Change-Id: Ic7384731bf9a1fa8b9602d4f1dbee7492db126c5