[JFFS2] Remove stray __exit from jffs2_compressors_exit()

It's used from the initfunc in case of failure too. We could actually do
with an '__initexit' for this kind of thing -- when built in to the
kernel, it could do with being dropped with the init text. We _could_
actually just use __init for it, but that would break if/when we start
dropping init text from modules. So let's just leave it as it was for now,
and mutter a little more about random 'janitorial' fixes from people who
aren't paying attention to what they're doing.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>