Remove workaround for a bug in dart2wasm (flutter#151603)

The bug in dart2wasm that required this workaround should be fixed now.

Issue dart-lang/sdk#56129

Author: mkustermann

packages/flutter/lib/src/widgets/focus_manager.dart

@@ -2222,9 +2222,6 @@ FocusNode? get primaryFocus => WidgetsBinding.instance.focusManager.primaryFocus
 String debugDescribeFocusTree() {
   String? result;
   assert(() {
-    // TODO(yjbanov): remove this once https://github.com/dart-lang/sdk/issues/56129 has been fixed.
-    // ignore: unnecessary_statements
-    FocusManager.instance.toStringDeep;
     result = FocusManager.instance.toStringDeep();
     return true;
   }());