Backport #32940

* Update the default value for $enable-deprecation-messages

As seen in the https://github.com/twbs/bootstrap/blob/v4-dev/scss/_variables.scss,
the `$enable-deprecation-messages` variable is set to `true` by default.

site/content/docs/4.6/getting-started/theming.md

@@ -304,7 +304,7 @@ You can find and customize these variables for key global options in Bootstrap's
 | `$enable-print-styles`                       | `true` (default) or `false`        | Enables styles for optimizing printing. |
 | `$enable-responsive-font-sizes`              | `true` or `false` (default)        | Enables [responsive font sizes]({{< docsref "/content/typography#responsive-font-sizes" >}}). |
 | `$enable-validation-icons`                   | `true` (default) or `false`        | Enables `background-image` icons within textual inputs and some custom forms for validation states. |
-| `$enable-deprecation-messages`               | `true` or `false` (default)        | Set to `true` to show warnings when using any of the deprecated mixins and functions that are planned to be removed in `v5`. |
+| `$enable-deprecation-messages`               | `true` (default) or `false`        | Set to `false` to hide warnings when using any of the deprecated mixins and functions that are planned to be removed in `v5`. |
 
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