Remove bad kmem_free() oversight from previous zfsdev_state_list patch

I forgot to remove the corresponding kmem_free() from zfs_kmod_fini() in
9a14ce43c3d6a9939804215bbbe66de5115ace42. Clang's static analyzer did
not complain, but the Coverity scan that was run after the patch was
merged did.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reported-by: Coverity (CID-1535275)
Closes #14556