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>

scripts/Makefile.clean

@@ -88,11 +88,6 @@ PHONY += $(subdir-ymn)
 $(subdir-ymn):
 	$(Q)$(MAKE) $(clean)=$@
 
-# If quiet is set, only print short version of command
-
-cmd = @$(if $($(quiet)cmd_$(1)),echo '  $($(quiet)cmd_$(1))' &&) $(cmd_$(1))
-
-
 # Declare the contents of the .PHONY variable as phony.  We keep that
 # information in a variable se we can use it in if_changed and friends.