kbuild: remove a stale comment about cleaning in link-vmlinux.sh

Remove the left-over of commit 51eb95e2 ("kbuild: Don't remove
link-vmlinux temporary files on exit/signal").
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/link-vmlinux.sh

@@ -201,7 +201,6 @@ sorttable()
 	${objtree}/scripts/sorttable ${1}
 }
 
-# Delete output files in case of error
 cleanup()
 {
 	rm -f .btf.*