Merge pull request #4615 from greg0ire/remove-docs-about-user-provide…

…d-pdo

docs/en/reference/configuration.rst

@@ -137,7 +137,6 @@ interfaces to use. It can be configured in one of three ways:
 -  ``driverClass``: Specifies a custom driver implementation if no
    'driver' is specified. This allows the use of custom drivers that
    are not part of the Doctrine DBAL itself.
--  ``pdo``: Specifies an existing PDO instance to use.
 
 Wrapper Class
 ~~~~~~~~~~~~~
@@ -155,11 +154,6 @@ as the credentials to use. The connection details can differ
 depending on the used driver. The following sections describe the
 options recognized by each built-in driver.
 
-.. note::
-
-    When using an existing PDO instance through the ``pdo``
-    option, specifying connection details is obviously not necessary.
-
 pdo_sqlite
 ^^^^^^^^^^