[examples] updated DARPA SUBOFF link

[marcvivesmassana]

Note

Low Risk
Single-string URL change in an example; low risk aside from potentially breaking the example if the new S3 object path is incorrect.

Overview
Updates the DARPA_SUBOFF example to point its url.geometry download link at DARPA_SUBOFF.STEP instead of the older DARPA.STEP S3 object.

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