NYC cleanup: remove cts_download.sh since unused

BUG=b:151958629
TEST=None

Change-Id: Ifc6dc2c07c49753ebb5eab1728ed8633fffebcb7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/2135932
Commit-Queue: Victor Hsieh <victorhsieh@chromium.org>
Commit-Queue: Rohit Makasana <rohitbm@chromium.org>
Tested-by: Victor Hsieh <victorhsieh@chromium.org>
Auto-Submit: Victor Hsieh <victorhsieh@chromium.org>
Reviewed-by: Rohit Makasana <rohitbm@chromium.org>