Remove SplashICCTransform altogether from drawImage functionality

The whole purpose of SplashICCTransform is to draw images with an ICC colorspace. Unfortunately, this just doubles functionality from GfxImageColorMap which can already call get{RGB,CMYK,...}Line of the respective GfxICCBasedColorSpace, which does the color transform anyway.

Note that this commutes the order in which the image is scaled and transformed in Splash::drawImage. So far, it is first scaled then the ICC transform applied. Now, it will be the other way around, first color transformed then scaled. This can potentially have speed implications, as well as changes the color space in which the bilinear interpolation is done for upscaling.

@thomas Any thoughts on this?