Replace old implicit animation codelab with updated combined one (#12630)

- Removes the old [Implicit animations
codelab](https://docs.flutter.dev/codelabs/implicit-animations) that was
hosted directly on the site.
- Redirects the link and updates mentions to point to John and Justin's
more recently updated [Animations in Flutter
codelab](https://codelabs.developers.google.com/advanced-flutter-animations).

Author: parlough

.github/dependabot.yml

@@ -42,7 +42,6 @@ updates:
       - "/examples/animation/animate3"
       - "/examples/animation/animate4"
       - "/examples/animation/animate5"
-      - "/examples/animation/implicit"
       - "/examples/cookbook/animation/animated_container"
       - "/examples/cookbook/animation/opacity_animation"
       - "/examples/cookbook/animation/page_route_animation"