Remove a deprecated description.

reference/catalog/index.md

@@ -101,7 +101,7 @@ tables.
 Droonga Engine can be extended by writing plugin scripts.
 In most cases, a series of plugins work cooperatively to
 achieve required behaviors.
-So, basically plugins are organized by behaviors.
+So, plugins are organized by behaviors.
 Each behavior can be attached to datasets and/or tables by
 adding "plugins" section to the corresponding entry in the catalog.
 
@@ -111,9 +111,6 @@ when adapting messages.
 When adapting an incoming message, plugins are applied in forward order
 whereas those are applied in reverse order when adapting an outgoing message.
 
-Although plugins can also be assigned by each stage of data processing
-(e.g. "collector", "planner"), this manner will be deprecated in the future version.
-
 ## Example
 
 Consider the following case: