ipmi: remove unused target and action in Makefile

Kbuild system handles this automatically.

Signed-off-by: Denis Cheng <crquan@gmail.com>
Cc: Corey Minyard <minyard@acm.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>