fix(test): Fix the StaleElementReference in 'rp listed in apps, can be deleted' (#4979) r=vladikoff
fix(test): Fix the StaleElementReference in 'rp listed in apps, can be deleted' (#4979) r=vladikoff

wait for the element to be gone or else it's possible for the subsequent
`click` can fail with a StaleElementReference because click on 123Done's
button happens, the XHR request takes a bit of time, the reference to the
321 Done button is fetched, the XHR request completes and updates the DOM,
making the reference to the 321 Done button stale.

fixes #4968
shane-tomlinson/fxa-content-server,mozilla/fxa-content-server,mozilla/fxa-content-server,shane-tomlinson/fxa-content-server,mozilla/fxa-content-server,shane-tomlinson/fxa-content-server