base-files: remove shebang from uci-defaults files

uci-defaults are sourced and non-executable, so they do not require
a shebang.

While at it, apply consistent naming scheme.

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

package/base-files/files/etc/uci-defaults/10_migrate-shadow

@@ -1,5 +1,3 @@
-#!/bin/sh
-
 ppwd="$(sed -ne '/^root:/s/^root:\([^:]*\):.*$/\1/p' /etc/passwd)"
 spwd="$(sed -ne '/^root:/s/^root:\([^:]*\):.*$/\1/p' /etc/shadow)"