Easiest way is to change the opacity - assuming you don't mind losing the greyish background as well.
In the rpg_scenes.js file find the Scene_Item create function below and add in the last line:
Scene_Item.prototype.create = function() {
Scene_ItemBase.prototype.create.call(this);
this.createHelpWindow();
this.createCategoryWindow();
this.createItemWindow();
this.createActorWindow();
this._itemWindow.opacity = 0;
};