app: drop history-narrative prose from Submit tab

The Submit tab carried a sentence explaining why there's no form
to fill in ("All five fields come from meta.json inside the zip,
no separate form to fill in."). To a launch visitor that explains
an absence that was never there; the right thing is to describe
the contract as it stands, not to narrate a removal.

Cut the sentence; keep the one useful half as a "Consent." line
documenting that agree_to_publish: true in meta.json is the
consent gate.

app.py

@@ -74,9 +74,8 @@ stack, put it here or in `notes`.
 and stripped to a single line. Shown in the per-submission detail view,
 not in the main leaderboard table.
 
-All five fields come from `meta.json` inside the zip, no separate
-form to fill in. Setting `agree_to_publish: true` in `meta.json` is
-your consent to publish on the public leaderboard.
+**Consent.** `"agree_to_publish": true` in `meta.json` is your consent
+to publish the resulting row on the public leaderboard.
 """
         )
         zip_in = gr.File(label="Submission ZIP", file_types=[".zip"])