kbuild: remove redundant '.*.cmd' pattern from make distclean

'.*.cmd' files are cleaned-up by "make clean".
The same pattern in "make distclean" is unnecessary.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>