Unfortunately there is no way to revert your game to a previous version. In order to even play Destiny you must have the most up to date version. The DLCs you install are just license keys which unlock content for you. Uninstalling a DLC will not affect what the vendors have for sale.
Vendor weapons are control on Bungie's end. Uninstalling ROI will not allow you to get the weapons/gear vendors had during TTK. Every so often, usually with larger updates, vendor supplies change.