Removed empty arguments

Author: Nyholm

Resources/config/plugins.xml

@@ -6,12 +6,10 @@
     <services>
         <service id="httplug.plugin.content_length" class="Http\Client\Plugin\ContentLengthPlugin" public="false" />
         <service id="httplug.plugin.decoder" class="Http\Client\Plugin\DecoderPlugin" public="false">
-            <argument />
         </service>
         <service id="httplug.plugin.error" class="Http\Client\Plugin\ErrorPlugin" public="false" />
         <service id="httplug.plugin.logger" class="Http\Client\Plugin\LoggerPlugin" public="false">
             <argument type="service" id="logger"/>
-            <argument />
         </service>
         <service id="httplug.plugin.redirect" class="Http\Client\Plugin\RedirectPlugin" public="false" />
         <service id="httplug.plugin.retry" class="Http\Client\Plugin\RetryPlugin" public="false" />