autotests: Drop testBufferSizeChange
testXdgShellWindow already tests intricate subsurface size changes. The surface pixmaps are handled differently now too, so the test is not useful as it used to be 4 or 5 years ago.
testXdgShellWindow already tests intricate subsurface size changes. The surface pixmaps are handled differently now too, so the test is not useful as it used to be 4 or 5 years ago.