swrast: Remove _swrast_write_zoomed_index_span and associated code

After removing support for CopyPixels and DrawPixels involving
color-index buffers, _swrast_write_zoomed_index_span is no longer
used.  Removed it and all the support for COLOR_INDEX formats in zoom_span.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
2 files changed