linux-phytec-fsl

kbuild: Remove duplicate $(cmd) definition in Makefile.clean

Makefile.clean includes Kbuild.include since commit 371fdc77
(kbuild: collect shorthands into scripts/Kbuild.include), so there is no
need for a local copy.

Signed-off-by: Michal Marek <mmarek@suse.cz>