pan/decode: Cleanup pandecode_jc

Some of this code is, to put it mildly, impossibly ancient horsedropping
crazy cruft.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3836>
2 files changed