Revert "dix: Work around non-premultiplied ARGB cursor data harder"
This reverts commit b45c74f0.
It broke the cursor in other games. Apparently those use cursor data with premultiplied alpha, but with some pixels having r/g/b values larger than the alpha value (which corresponds to original r/g/b values > 1.0), triggering the workaround.
Seems the cure turned out worse than the disease, so revert.