minor #8507 Deprecated loadClassCache() method (javiereguiluz)

This PR was merged into the 3.3 branch.

Discussion
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Deprecated loadClassCache() method

This fixes #7337. I didn't found any other occurrence of the deprecated classes/methods mentioned in the related issue. In #7819 we're taking care of the deprecation of `addClassesToCompile()`.

Commits
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7e7a945 Deprecated loadClassCache() method

Author: xabbuh

debug/debugging.rst

@@ -61,6 +61,11 @@ cache files, or you can change the extension used by Symfony for these files::
 
     $kernel->loadClassCache('classes', '.php.cache');
 
+.. versionadded:: 3.3
+    The ``loadClassCache()`` was deprecated in Symfony 3.3 and removed in
+    Symfony 4.0. No alternative is provided because this feature is useless
+    when using PHP 7 or higher.
+
 Useful Debugging Commands
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