Revert "nine: cheat-disable clipping"

This reverts commit ca128bab40f7584f67e76a40fec5177ca5080ca2.

Because it doesn't work, the 'w' coordinate has to be preserved
but it must not affect the transformation, which is impossible
without actually disabling the viewport transformation.

Conflicts:

	src/gallium/state_trackers/nine/nine_ff.c
nine/state: a better (arguably) cheat to disable clipping

Because it requires driver support.
nvc0: disable clipping hack if viewport.scale.w == 0
gallium/draw: support hack to disable clipping