minor #14101 [Configuration] improve description for ignoreExtraKeys on ArrayNodeDefinition (cordoval)

This PR was merged into the 2.3 branch.

Discussion
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[Configuration] improve description for ignoreExtraKeys on ArrayNodeDefinition

|Q            |A  |
|---          |---|
|Bug Fix?     |y  |
|New Feature? |n  |
|BC Breaks?   |n  |
|Deprecations?|n  |
|Tests Pass?  |y  |
|Fixed Tickets| #13957  |
|License      |MIT|
|Doc PR       |   |

Commits
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b735022 [Configuration] improve description for ignoreExtraKeys on ArrayNodeDefinition

Author: fabpot

Definition/Builder/ArrayNodeDefinition.php

@@ -287,9 +287,10 @@ public function performNoDeepMerging()
      * Allows extra config keys to be specified under an array without
      * throwing an exception.
      *
-     * Those config values are simply ignored. This should be used only
-     * in special cases where you want to send an entire configuration
-     * array through a special tree that processes only part of the array.
+     * Those config values are simply ignored and removed from the
+     * resulting array. This should be used only in special cases where
+     * you want to send an entire configuration array through a special
+     * tree that processes only part of the array.
      *
      * @return ArrayNodeDefinition
      */