feat: remove wrong include

Author: naetherm

engine/samples/CMakeLists.txt

@@ -25,7 +25,6 @@
 re_add_subdirectory(00_hello_world)
 re_add_subdirectory(01_system_information)
 re_add_subdirectory(05_sample_plugin)
-re_add_subdirectory(06_sample_plugin_app)
 re_add_subdirectory(10_frontend)
 re_add_subdirectory(11_frontend_multiwindow)
 re_add_subdirectory(12_gui)