docs: trim attribution examples to Google and Meta only

Remove TikTok and OpenAI examples — additional platform examples
will be included in the PR description.

Author: jamesandersen

docs/specification/attribution.md

@@ -185,59 +185,3 @@ The merchant passes `event_id` and `fbp` (from `session_id`) to their
 Conversions API integration. The shared `event_id` prevents duplicate event
 counting between the platform's first-party event and the merchant's server-side
 event.
-
-### TikTok (TikTok Ads)
-
-A user discovers a product via a TikTok ad and completes the purchase through
-an agentic flow:
-
-```json
-{
-  "attribution": {
-    "platform": "com.tiktok",
-    "dedup_keys": {
-      "event_id": "evt_tt_xyz789abc012"
-    },
-    "utm": {
-      "utm_source": "tiktok",
-      "utm_medium": "paid_social",
-      "utm_campaign": "spring_launch_2026",
-      "utm_content": "5555555555",
-      "utm_id": "1234567890"
-    },
-    "custom": {
-      "click_id": "E.C.P.abcdef123456...",
-      "ad_group_id": "9876543210",
-      "placement": "TikTok_For_You_Feed"
-    }
-  }
-}
-```
-
-### OpenAI (ChatGPT Shopping)
-
-A user asks ChatGPT for product recommendations and purchases through agentic
-checkout. Even without a traditional campaign, the platform provides attribution
-context:
-
-```json
-{
-  "attribution": {
-    "platform": "com.openai",
-    "dedup_keys": {
-      "event_id": "evt_oai_def456ghi789"
-    },
-    "utm": {
-      "utm_source": "chatgpt",
-      "utm_medium": "agentic",
-      "utm_campaign": "shopping_recommendations"
-    },
-    "custom": {
-      "session_token": "chatgpt_sess_abc123..."
-    }
-  }
-}
-```
-
-This shows the extension works for any referral channel, not just paid
-advertising.