GOB: Remove the last remnants of Draw::_vgaSmallPalette

Draw::_vgaSmallPalette was supposed to be a 16-color VGA
palette / EGA palette, but we've been using the first 16
entries of Draw::_vgaPalette for that for ages now.

The only parts where we didn't were codepaths never
actually taken in the gob games, so for the sake of
clarity (and fixing Coverity issues), this commit removes
those as well.

Fixes Coverity issues 1192648 and 1192649.