treewide: remove execute bit and shebang from board.d files

So far, board.d files were having execute bit set and contained a
shebang. However, they are just sourced in board_detect, with an
apparantly unnecessary check for execute permission beforehand.

Replace this check by one for existance and make the board.d files
"normal" files, as would be expected in /etc anyway.

Note:

This removes an apparantly unused '#!/bin/sh /etc/rc.common' in
target/linux/bcm47xx/base-files/etc/board.d/01_network

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

package/base-files/files/bin/board_detect

@@ -6,7 +6,7 @@ CFG=$1
 
 [ -d "/etc/board.d/" -a ! -s "$CFG" ] && {
 	for a in $(ls /etc/board.d/*); do
-		[ -x $a ] || continue;
+		[ -s $a ] || continue;
 		$(. $a)
 	done
 }

package/base-files/files/etc/board.d/99-default_network

@@ -1,4 +1,3 @@
-#!/bin/sh
 #
 # Copyright (C) 2013-2015 OpenWrt.org
 #