In the product manager itself, you actually need to remove the product through the AdminCP, not just delete the files. When you uninstall it, it executes the uninstall code that does the appropriate DB modifications and stops your forum from looking for those tables.

First, put the files back.

Then, ACP -> Plugins and Products -> Product Manager. Find the product in the list, and pick Uninstall from the dropdown on the right.

Unfortunately, since you dropped the tables the product uninstaller might die on you since it will still be looking for them. You MIGHT be able to just create two new blank tables with the same names to get the uninstaller to cycle through, but get a second opinion on that.