Update blockquote migration docs to reflect #22949

Fixes #25669, closes #25779.

Author: mdo

docs/4.0/migration.md

@@ -132,7 +132,7 @@ New to Bootstrap 4 is the [Reboot]({{ site.baseurl }}/docs/{{ site.docs_version
 - Moved all `.text-` utilities to the `_utilities.scss` file.
 - Dropped `.page-header` as, aside from the border, all its styles can be applied via utilities.
 - `.dl-horizontal` has been dropped. Instead, use `.row` on `<dl>` and use grid column classes (or mixins) on its `<dt>` and `<dd>` children.
-- Custom `<blockquote>` styling has moved to classes—`.blockquote` and the `.blockquote-reverse` modifier.
+- Redesigned blockquotes, moving their styles from the `<blockquote>` element to a single class, `.blockquote`. Dropped the `.blockquote-reverse` modifier for text utilities.
 - `.list-inline` now requires that its children list items have the new `.list-inline-item` class applied to them.
 
 ### Images