[FL-3435] External apps removed (#2934)

Co-authored-by: Aleksandr Kutuzov <alleteam@gmail.com>

site_scons/commandline.scons

@@ -226,7 +226,6 @@ vars.AddVariables(
             ("applications/settings", False),
             ("applications/system", False),
             ("applications/debug", False),
-            ("applications/external", False),
             ("applications/examples", False),
             ("applications/drivers", False),
             ("applications_user", False),