BoUT2: Add shadow PIXEL shaders dumped from game

Finally worked out what I was doing wrong with these before (ps_2_0 doesn't
have anywhere near as many constant registers as ps_3_0, and didn't seem to get
automatically overridden by HelixMod). Add the pixel shaders and remove the
vertex shaders.
BoUT2: Disable shadows in Wilbur area, this time with pixel shaders

HelixMod didn't seem to pick these up as ps_2_0 for whatever reason and
ShaderConverter doesn't convert pixel shaders (I should write my own), so this
commit also includes a manual ps_2_0 -> ps_3_0 conversion because I did that at
the same time and can't be arsed splitting this commit into two.