test-lib: Work around missing sum on Windows

Signed-off-by: Johannes Sixt <j6t@kdbg.org>

t/t1002-read-tree-m-u-2way.sh

@@ -10,12 +10,6 @@ This is identical to t1001, but uses -u to update the work tree as well.
 '
 . ./test-lib.sh
 
-sum ./test-lib.sh >/dev/null 2>&1 || {
-	function sum () {
-		md5sum "$@"
-	}
-}
-
 _x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
 _x40="$_x40$_x40$_x40$_x40$_x40$_x40$_x40$_x40"
 compare_change () {

t/test-lib.sh

@@ -646,5 +646,8 @@ case $(uname -s) in
 	find () {
 		/usr/bin/find "$@"
 	}
+	sum () {
+		md5sum "$@"
+	}
 	;;
 esac