MIPS: Remove useless comment about kprobe from arch/mips/Makefile

The commit c1bf207d (kernel.org) rsp.
58e9ad32a48dce37ffeea912f55bd1c94b85ad7f (lmo) [MIPS: kprobe: Add support]
introduced a useless comment.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: David Daney <ddaney@caviumnetworks.com>
Patchwork: https://patchwork.linux-mips.org/patch/1765/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>