Crowdsignal blocks don't undo

If you add a Crowdsignal block and then immediately press undo, the block isn't removed. Instead it takes 5 or 6 undos before it disappears.

I suspect that internally it is creating several invisible undo events, maybe as a result of successive `setAttributes`.

Tested with latest version on wp.com

No file or test is named; start by reproducing the issue with a Crowdsignal block and inspect the block's undo behavior around the successive `setAttributes` calls mentioned in the report. Done means adding the block and pressing undo once removes it completely, without requiring repeated undos.

Written by the indexing model from the issue text.