bug #11613 Remove $context argument from supportsNormalization in example (pskt)

This PR was merged into the 3.4 branch.

Discussion
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Remove $context argument from supportsNormalization in example

This PR removes `$context` argument from supportsNormalization() method.

`NormalizerInterface` defines only `$data` and `$format` arguments (see https://github.com/symfony/symfony/blob/3.4/src/Symfony/Component/Serializer/Normalizer/NormalizerInterface.php#L51)

Commits
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cd1fa25 Remove $context argument from example code

Author: OskarStark

serializer/custom_normalizer.rst

@@ -47,7 +47,7 @@ to customize the normalized data. To do that, leverage the ``ObjectNormalizer``:
             return $data;
         }
 
-        public function supportsNormalization($data, $format = null, array $context = [])
+        public function supportsNormalization($data, $format = null)
         {
             return $data instanceof Topic;
         }