Merge pull request #8910 from kenjis/docs-uploaded_files.rst

docs: simplify explanation in uploaded_files.rst

Author: kenjis

user_guide_src/source/libraries/uploaded_files.rst

@@ -83,12 +83,10 @@ this code and save it to your **app/Controllers** directory:
 
 .. literalinclude:: uploaded_files/002.php
 
-Since the value of a file upload HTML field doesn't exist, and is stored in the
-``$_FILES`` global, only :ref:`rules-for-file-uploads` can be used to validate
-the upload file with :doc:`validation`.
+Only the :ref:`rules-for-file-uploads` can be used to validate uploaded files.
 
-The rule ``required`` cannot be used either, so if the file is required, use
-the rule ``uploaded`` instead.
+Therefore, the rule ``required`` cannot be used either, so if the file is required,
+use the rule ``uploaded`` instead.
 
 Note that an empty array (``[]``) is passed as the first argument to
 ``$this->validateData()``. It is because the file validation rules get the data