build: remove duplicated tree example code (#17844)

The tree demo app had a bunch of code that was duplicated with examples from `components-examples`. These changes delete that code and use the example components instead.

Author: crisbeto

src/dev-app/tree/BUILD.bazel

@@ -9,10 +9,6 @@ ng_module(
         "**/*.html",
     ]) + [
         ":tree_demo_scss",
-        ":checklist_nested_tree_demo_scss",
-        ":checklist_tree_demo_scss",
-        ":dynamic_tree_demo_scss",
-        ":loadmore_tree_demo_scss",
     ],
     deps = [
         "//src/cdk/tree",
@@ -34,23 +30,3 @@ sass_binary(
     name = "tree_demo_scss",
     src = "tree-demo.scss",
 )
-
-sass_binary(
-    name = "checklist_nested_tree_demo_scss",
-    src = "checklist-tree-demo/checklist-nested-tree-demo.scss",
-)
-
-sass_binary(
-    name = "checklist_tree_demo_scss",
-    src = "checklist-tree-demo/checklist-tree-demo.scss",
-)
-
-sass_binary(
-    name = "dynamic_tree_demo_scss",
-    src = "dynamic-tree-demo/dynamic-tree-demo.scss",
-)
-
-sass_binary(
-    name = "loadmore_tree_demo_scss",
-    src = "loadmore-tree-demo/loadmore-tree-demo.scss",
-)