kbuild: clean up ${quiet} checks in shell scripts

There were efforts to make 'make -s' really silent when it is a
warning-free build.

The conventional way was to let a shell script check ${quiet}, and if
it is 'silent_', suppress the stdout by itself.

With the previous commit, the 'cmd' takes care of it now. The 'cmd' is
also invoked from if_changed, if_changed_dep, and if_changed_rule.

You can omit ${quiet} checks in shell scripts when they are invoked
from the 'cmd' macro.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kernel/gen_kheaders.sh

@@ -56,9 +56,7 @@ if [ -f kernel/kheaders.md5 ] &&
 		exit
 fi
 
-if [ "${quiet}" != "silent_" ]; then
-       echo "  GEN     $tarfile"
-fi
+echo "  GEN     $tarfile"
 
 rm -rf $cpio_dir
 mkdir $cpio_dir