minor symfony#11034 remove the mention of .yml (OskarStark)

This PR was squashed before being merged into the 4.2 branch (closes symfony#11034).

Discussion
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remove the mention of .yml

we should not promote the usage of .yml anymore

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Commits
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4e7092d remove the mention of .yml

Author: javiereguiluz

configuration/configuration_organization.rst

@@ -78,7 +78,7 @@ Mix and Match Configuration Formats
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Configuration files can import files defined with any other built-in configuration
-format (``.yaml`` or ``.yml``, ``.xml``, ``.php``, ``.ini``):
+format (``.yaml``, ``.xml``, ``.php``, ``.ini``):
 
 .. configuration-block::
 

reference/configuration/framework.rst

@@ -723,7 +723,7 @@ type
 
 The type of the resource to hint the loaders about the format. This isn't
 needed when you use the default routers with the expected file extensions
-(``.xml``, ``.yml`` or ``.yaml``, ``.php``).
+(``.xml``, ``.yaml``, ``.php``).
 
 http_port
 .........