Revert "mode_flag: make it empty array"

This reverts commit afe564f9a961f608d9c2b89aebe25e1c1c10063b.

Reason for revert:
Causes a breakage with mod_image_for_recovery.sh on all legacy builders. See https://bugs.chromium.org/p/chromium/issues/detail?id=1180660#c7

Original change's description:
> mode_flag: make it empty array
>
> Since bash-4.4, "${array[@]:+${array[@]}}" resolves to "", whereas
> before it was resolving to an empty array.
> _check_mount_image_flags expects an empty array, make it so.
>
> BUG=None
> TEST=unit tests
>
> Change-Id: I9de8439bcd8e20098b162c21dd03b6adcc3ac856
> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2685277
> Commit-Queue: Sergey Frolov <sfrolov@google.com>
> Tested-by: Sergey Frolov <sfrolov@google.com>
> Reviewed-by: Mike Frysinger <vapier@chromium.org>

Cq-Depend: chromium:2711674
Cq-Depend: chromium:2710230

BUG=chromium:1180660
Change-Id: I7747bb1bfdf4d35b5ca593eb239f4fc1d00745fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2710149
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
1 file changed