ref(analytics): Update amplitude analytics docs (#1253)

src/docs/analytics.mdx

@@ -101,18 +101,8 @@ analytics.record(
 
 Run the tests that touch the endpoint to ensure everything is Gucci.
 
-### Step 3: Add it to ETL
-
-To also send the analytics event in Amplitude, add the event to this file: [https://github.com/getsentry/etl/blob/master/etl/operators/analytics_events_schema.py](https://github.com/getsentry/etl/blob/master/etl/operators/analytics_events_schema.py)
-
-```jsx
-'my_backend_event.sent': { // Needs to match the `type` field in the class you created in step 1
-    'name': 'My Backend Event', // The event name in Amplitude
-    'uid_field': 'target_user_id' // Optional. Field name that represents the user id of the event.
-},
-```
-
-Note that in the future this will change so that by default, all events will go to Amplitude.
+### Step 3: 
+By default, a new event type is aggregated and sent to Amplitude as long as there is a user_id sent along with the event. If you would like to send events unaggregated, refer to [our Amplitude aggregation docs](https://github.com/getsentry/etl/blob/master/documentation/amplitude_analytics.md)
 
 ## Route-Based Frontend Analytics