JFS: Remove incorrect kgdb define

jfs_debug.h uses an incorrect CONFIG_KERNEL_ASSERT ifdef to redefine the
assert macro for kgdb use.  I believe the code worked a long time ago, but
today it's not a valid config option.  Since I'm not aware of anybody
interested in debugging jfs with kgdb, it should just be removed.

Thanks to Robert P. J. Day for reporting this.

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>