jfs: remove unused declarations for jfs

extRealloc(), xtRelocate(), xtDelete() and extFill() have been
removed since commit e471e594

 ("fs/jfs: Remove dead code"),
so remove them.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>