Revert "Use nested blocks for quotes (#6054)"

[ellatrix]

This reverts commit 853900d.

[jasmussen]

Note that the citation issue with the quote that has nested blocks is not unique to this block, and you can actually surface the cite still, just have to select the quote block. This is hard, because the block breadcrumb toolbar hasn't worked as intended. But I'm working on a new approach to make it simpler to select blocks and their parents in try/alternate-hover-approach (that branch is waaay WIP), but essentially that would mean we could go back to having nested blocks in the quote.

[mcsf]

Thanks for reverting. Let's wait until all the stars align (design and UX, more technical support for all things nested) so we can get this back in.