[Files app] Remove ErrorDialog dead code

ErrorDialog was only used for ActionsModel as a dependency but nothing
really calls errorDialog instance, so remove it.

I noticed it when trying to convert it to ES6 class.

Change-Id: I4b6096b20ae0d8ee8ec36849cc822a6cc268253a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1619447
Commit-Queue: François Degros <fdegros@chromium.org>
Auto-Submit: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: François Degros <fdegros@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661540}
7 files changed