docs: remove unused directories in Structure

Author: kenjis

user_guide_src/source/installation/installing_composer.rst

@@ -86,7 +86,6 @@ Folders in your project after set up:
 
 - app, public, tests, writable
 - vendor/codeigniter4/framework/system
-- vendor/codeigniter4/framework/app & public
 
 Latest Dev
 ----------