scripts: remove scripts-wide shellcheck excludes

This removes script-wide shellcheck excludes to avoid unintentional
errors and moves the excludes to the scripts where they are necessary.

scripts/default_feeds.sh

+#!/bin/sh
+
 # list feeds which don't start with #
 DEFAULT_FEEDS="$(awk '!/^#/ {print $2}' openwrt/feeds.conf.default)"
+export DEFAULT_FEEDS

scripts/lint-sh.sh

@@ -24,5 +24,5 @@ find scripts -type f | while read -r file; do
 	is_scriptfile "$file" || continue
 
 	echo "Checking $file"
-	shellcheck -f gcc -x -e SC2154,SC1090,SC2181,SC2155,SC2148,SC2034,SC2148 "$file"
+	shellcheck -f gcc -x "$file"
 done

scripts/module_check.sh

 #!/bin/bash
+# shellcheck disable=SC2154
 
 set -e
 

scripts/modules.sh

+#!/bin/sh
+
+# shellcheck source=./modules
 . ./modules
+
 [ ! -f "$GLUON_SITEDIR"/modules ] || . "$GLUON_SITEDIR"/modules
 
 # shellcheck disable=SC2086

scripts/sha256sum.sh

@@ -15,6 +15,7 @@ else
 	exit 1
 fi
 
+# shellcheck disable=SC2181
 [ "$?" -eq 0 ] || exit 1
 
 echo "$ret" | awk '{ print $1 }'

scripts/update.sh

 #!/bin/bash
+# shellcheck disable=SC2154
 
 set -e