Fixup experimental/federated_plugin (#1776)

Replaces https://github.com/flutter/samples/pull/1749

FYI @negotoyolo

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tool/flutter_ci_script_beta.sh

@@ -26,13 +26,10 @@ declare -ar PROJECT_NAMES=(
     "desktop_photo_search/material"
     "experimental/context_menus"
     "experimental/element_embedding_demo"
-    # TODO(DomesticMouse): 'setMockMethodCallHandler' is deprecated and shouldn't be used.
-    # "experimental/federated_plugin/federated_plugin"
-    # TODO(DomesticMouse): 'setMockMethodCallHandler' is deprecated and shouldn't be used.
-    # "experimental/federated_plugin/federated_plugin/example"
+    "experimental/federated_plugin/federated_plugin"
+    "experimental/federated_plugin/federated_plugin/example"
     "experimental/federated_plugin/federated_plugin_macos"
-    # TODO(DomesticMouse): 'setMockMethodCallHandler' is deprecated and shouldn't be used.
-    # "experimental/federated_plugin/federated_plugin_platform_interface"
+    "experimental/federated_plugin/federated_plugin_platform_interface"
     "experimental/federated_plugin/federated_plugin_web"
     "experimental/federated_plugin/federated_plugin_windows"
     "experimental/linting_tool"