minor #19960 [ExpressionLanguage] Remove misleading warning (valepu)

This PR was submitted for the 7.1 branch but it was merged into the 5.4 branch instead.

Discussion
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[ExpressionLanguage] Remove misleading warning

Fixes #17978

The warning I am removing was created after #8259 but the issue used an incorrect regex to show a potential problem which doesn't exist.

In my issue I show that it's not actually possible to inject control characters. I would still suggest for someone more involved in symfony development to investigate further, if the expression language is used in the security component this would need more than just a warning

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Commits
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e9d242d Remove misleading warning

Author: javiereguiluz

components/expression_language.rst

@@ -112,13 +112,6 @@ expressions (e.g. the request, the current user, etc.):
 * :doc:`Variables available in service container expressions </service_container/expression_language>`;
 * :ref:`Variables available in routing expressions <routing-matching-expressions>`.
 
-.. caution::
-
-    When using variables in expressions, avoid passing untrusted data into the
-    array of variables. If you can't avoid that, sanitize non-alphanumeric
-    characters in untrusted data to prevent malicious users from injecting
-    control characters and altering the expression.
-
 .. _expression-language-caching:
 
 Caching