minor #16883 [Filesystem] filesystem > readlink: remove function declaration (alexislefebvre)

This PR was squashed before being merged into the 4.4 branch.

Discussion
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[Filesystem] filesystem > readlink: remove function declaration

I think that `public function` was confusing here: we don't want to define this method but we want to know how to use it.

The code will be more consistent with the other examples.

Commits
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47cb76d [Filesystem] filesystem > readlink: remove function declaration

Author: javiereguiluz

components/filesystem.rst

@@ -214,9 +214,7 @@ systems (unlike PHP's :phpfunction:`readlink` function)::
 
 Its behavior is the following::
 
-    public function readlink($path, $canonicalize = false)
-
-* When ``$canonicalize`` is ``false``:
+* When ``$canonicalize`` is ``false`` (the default value):
     * if ``$path`` does not exist or is not a link, it returns ``null``.
     * if ``$path`` is a link, it returns the next direct target of the link without considering the existence of the target.