Remove reference to removed docs entry

Krzysztof Socha · Krzysztof Socha · commit db3ee71f7d83 · 2018-08-03T14:33:04.000+01:00
diff --git a/docs/upgrade/3.0.rst b/docs/upgrade/3.0.rst
@@ -304,7 +304,7 @@ Placeholders are pre-fillable with default plugins
 
 In CMS_PLACEHOLDER_CONF, for each placeholder configuration, you can specify
 via 'default_plugins' a list of plugins to automatically add to the
-placeholder if empty. See :ref:`default_plugins in CMS_PLACEHOLDER_CONF <placeholder_default_plugins>`.
+placeholder if empty. See default_plugins in CMS_PLACEHOLDER_CONF.
 
 Custom modules and plugin labels in the toolbar UI
 ==================================================
