Remove cros_workon implementation

Leave a helpful hint to developers to update their chroot if haven't
rebuilt their chroot recently.

BUG=brillo:817
TEST=exit chroot, enter chroot, cros_workon list-all works

CQ-DEPEND=CL:266773
Change-Id: I6f7fc646cde0062526feaba6b6fd5023ab8d4576
Reviewed-on: https://chromium-review.googlesource.com/266753
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
Tested-by: Christopher Wiley <wiley@chromium.org>
1 file changed