Possible memory leak where `did-update` render modifier runs on destroyed rows

[nwhittaker]

1. Visit https://ember-twiddle.com/910cbd741907663265e1ac93d4c8600e.
2. Scroll to the bottom of the list of inputs and make a change to the input in the last row. This will trigger an update modifier on each row to run.
3. Open the console and see several error messages showing the update modifier ran on some rows that no longer exist in the DOM and are now instead inside a document fragment.

I was expecting the did-update modifier to only run on elements that exist in the DOM.

Reproduced in both 2.1.0 and 3.0.0-1.