Remove hack from jpeg code.

When I developped the original implementation of Pokemon Stadium Japan jpeg decoding ucode
I tested it with Rice video plugin and cheated a little bit to get some sensible results
(I changed the UV rescaling a bit and perform erroneous Y1Y2 swapping). Other video plugin
didn't support YUV16 texture format so comparison wasn't possible.
Recently, I played a little bit with Glide64mk2 and noticed that without aformentionned hacks
the jpeg decoding was performing successfully. That's why I think there is a bug in Rice plugin
and that I can delete my hack from jpeg decoding ucode.
Refactor common jpeg decoding ucode.
Revert "Enable link time garbage collection when link time optimization is enabled"

Some linker on different platforms don't handle the garbage collection
correctly and create extreme bloated binaries. Therefore, leave it to the user
to enable this feature or not.
merged heads