Removing support files that are no longer needed

Hi Peter,

I'm about to modify the background-color tests (discussed in a separate thread) to be html-only reftests, eliminating the need for color swatch pngs they currently use.  Before I remove the pngs from the support folder in the repository, I'm checking that no other tests use them.  Is simply searching the /approved folder a good enough way to look this up? Or do I even need to do this?

Thanks,
-Rebecca