Fixing item_user migration primary keys

I had included item_id and user_id as primary keys to avoid duplications
but the command line to attach I am using does not duplicate.
Not only that, I got an error during migration of Multiple primary keys.

database/migrations/2018_09_08_192152_create_items_table.php

@@ -26,7 +26,6 @@ class CreateItemsTable extends Migration
             $table->increments('id');
             $table->integer('item_id');
             $table->integer('user_id');
-            $table->primary(['item_id', 'user_id']);
         });
     }