We had a bunch of old unused wrapper functions for each image codec that
would load a supported image with a given path. Nobody actually used
them, so let's just get rid of load_png(), load_gif(), etc.
Making a bitmap non-volatile after being volatile may fail to allocate
physical pages after the kernel stole the old pages in a purge.
This is different from the pages being purged, but reallocated. In that
case, they are simply replaced with zero-fill-on-demand pages as if
they were freshly allocated.
