Revert "[Material] Material theme builder (#313)" (#446)

This reverts commit 9a33d45.

Author: willlarche

.metadata

@@ -101,13 +101,6 @@ A collection of animation examples. The app starts with basic concepts like
 `AnimationController` and `Tween`, then progresses to transitions and
 advanced demos.
 
-#### [Material Theme Builder](material_theme_builder) _(Material team)_
-
-Build a Material Theme lets you create your own Material theme by customizing
-values for color, typography, and shape. See how these values are applied to
-Material components and discover how to implement your custom theme in your
-own projects.
-
 #### [Infinite list](infinite_list) _(Flutter team)_
 
 A sample implementation of the infinite list, a common UI pattern in which