Revert "libgui: Bring back support for mHeap-based screenshots"

This reverts commit bf9599eb0b91f226ec6d5223116b8b81b259b634.

This one was supposed to be a temporary fix, thats the reason i marked it -2. Unless you are 100% sure this doesnt break any devices we should revert it!

Change-Id: I024e55dca4257d63d6d8bd9738cccb99abe68086