Delete $OUT_OF_SOURCE_DIR under --force

The deletion of "$OUT_OF_SOURCE_DIR" had mistakenly been lumped
together with Yotta and then removed when Yotta support was removed.
Bring it back.

tests/scripts/all.sh

@@ -370,6 +370,7 @@ pre_parse_command_line () {
 
 pre_check_git () {
     if [ $FORCE -eq 1 ]; then
+        rm -rf "$OUT_OF_SOURCE_DIR"
         git checkout-index -f -q $CONFIG_H
         cleanup
     else