Remove custom PK for collectionuser.

apps/bandwagon/sql/collectionuser.sql

@@ -1,5 +0,0 @@
-ALTER TABLE `collections_users`
-    CHANGE COLUMN `id` `id` int(11) NOT NULL DEFAULT 0;
-
-ALTER TABLE `collections_users` DROP PRIMARY KEY,
-    ADD PRIMARY KEY(`collection_id`, `user_id`);