Docs: Remove mention about Safari's limited support flexbox gap

This callout was added a while ago and Safari has supported this for a while. It's safe to remove now.

site/content/docs/5.3/helpers/stacks.md

@@ -10,10 +10,6 @@ added:
 
 Stacks offer a shortcut for applying a number of flexbox properties to quickly and easily create layouts in Bootstrap. All credit for the concept and implementation goes to the open source [Pylon project](https://almonk.github.io/pylon/).
 
-{{< callout warning >}}
-**Heads up!** Support for gap utilities with flexbox was recently added to Safari, so consider verifying your intended browser support. Grid layout should have no issues. [Read more](https://caniuse.com/flexbox-gap).
-{{< /callout >}}
-
 ## Vertical
 
 Use `.vstack` to create vertical layouts. Stacked items are full-width by default. Use `.gap-*` utilities to add space between items.