minor symfony#6038 Fix symfony#6037 (zsturgess)

This PR was merged into the 3.0 branch.

Discussion
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Fix symfony#6037

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | >= 3.0
| Fixed tickets | symfony#6037

Removed an outdated caution block and rewrote an outdated paragraph.
Hopefully I've done everything correctly *crosses fingers*

Commits
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a7effb8 Fix symfony#6037

components/yaml/introduction.rst

@@ -135,16 +135,9 @@ It may also be convenient to use the
 
     $yaml = Yaml::parse(file_get_contents('/path/to/file.yml'));
 
-The :method:`Symfony\\Component\\Yaml\\Yaml::parse` static method takes a YAML
-string or a file containing YAML. Internally, it calls the
-:method:`Symfony\\Component\\Yaml\\Parser::parse` method, but enhances the
-error if something goes wrong by adding the filename to the message.
-
-.. caution::
-
-    Because it is currently possible to pass a filename to this method, you
-    must validate the input first. Passing a filename is deprecated in
-    Symfony 2.2, and will be removed in Symfony 3.0.
+The :method:`Symfony\\Component\\Yaml\\Yaml::parse` static method takes a YAML string.
+Internally, it constructs a :class:`Symfony\\Component\\Yaml\\Parser` object and calls
+the :method:`Symfony\\Component\\Yaml\\Parser::parse` method.
 
 .. _components-yaml-dump: