treewide: drop shebang from non-executable target files

This drops the shebang from all target files for /lib and
/etc/uci-defaults folders, as these are sourced and the shebang
is useless.

While at it, fix the executable flag on a few of these files.

This does not touch ar71xx, as this target is just used for
backporting now and applying cosmetic changes would just complicate
things.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ath25/base-files/lib/preinit/15_preinit_iface_atheros

@@ -1,5 +1,3 @@
-#!/bin/sh
-
 # reset button only supported on ar5315+ at the moment
 preinit_ip() {
 	if [ -z "$pi_ifname" ]; then