[symfony#9507] remove csv processor, it was added in 4.1

Author: xabbuh

configuration/external_parameters.rst

@@ -247,16 +247,6 @@ Symfony provides the following env var processors:
         sentry:
             dsn: '%env(resolve:SENTRY_DSN)%'
 
-``env(csv:FOO)``
-    Decodes the content of ``FOO``, which is a CSV-encoded string:
-
-    .. code-block:: yaml
-
-        parameters:
-            env(TRUSTED_HOSTS): "10.0.0.1, 10.0.0.2"
-        framework:
-           trusted_hosts: '%env(csv:TRUSTED_HOSTS)%'
-
 ``env(file:FOO)``
     Returns the contents of a file whose path is the value of the ``FOO`` env var: