Potential missed opportunity re. amp-analytics/amp-ad

**summary**

While fixing a new bug I introduced in amp-analytics, I noticed a codepath which I'm curious about.
Specifically that all analytic events fired for a destroyed embed are bailed out on.

https://github.com/ampproject/amphtml/blob/01f115a81355ca87ee5dab69127a710f8afcdc72/extensions/amp-analytics/0.1/amp-analytics.js#L643-L651

My question for those who know more about `` and ``: are there any instances where we'd still want to send the analytics event even though the embed has since been removed? If so, we probably want to make this check more granular and be able to tune it on a per event basis. My sources say this occurs many many times per day :)

cc @calebcordry / @micajuine-ho

Start with extensions/amp-analytics/0.1/amp-analytics.js at the linked lines and trace how destroyed amp-ad embeds cause analytics events to be bailed out. Determine whether any events should still be sent after removal; done requires a clear decision and, if warranted, defined per-event behavior.

Written by the indexing model from the issue text.