tables.sql: Correct lie about ct_params being unused

It is used by ContentTranslation to store things like
{"from":"es","to":"en"}

Change-Id: I880ecc74ab46dde2fa00ddb7baea08edeabcf676

maintenance/tables.sql

@@ -1835,7 +1835,7 @@ CREATE TABLE /*_*/change_tag (
   ct_rev_id int unsigned NULL,
   -- Tag applied
   ct_tag varchar(255) NOT NULL,
-  -- Parameters for the tag, presently unused
+  -- Parameters for the tag; used by some extensions
   ct_params blob NULL
 ) /*$wgDBTableOptions*/;