powerpc/configs/64s: Drop JFS Filesystem

Unlikely that anyone is still regularly using JFS, drop it from the
defconfig.

Suggested-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230420051609.1324201-2-mpe@ellerman.id.au