autotests: Use software rendering in testPointerInput
testPointerInput requires OpenGL compositing because it wants to test cursor push back in the window view effect and the window view effect is available only if OpenGL is supported.
On the other hand, ScreenEdgesTest::testPushBack() already tests similar scenario, so let's drop relevant test in testPointerInput to allow running it when using software rendering.
Edited by Vlad Zahorodnii