You can do the following. for the most clean uninstall

0. Stop all your webdb listeners.

1. Remove the directory of webdb from unix

rm -rf webdb

2. When you had installed the webdb, you would have created a repository on the database. There would be a user name
WEBSYS and remove that user and if you are sure that you had put this user unser a dedicated tablespace, you can drop that tablespace too. If not, just dropping the user would drop the entire webdb schema, that was created on the database

It had been a long time since I played with the webdb, but quiet sure that this would do the most clean install to my knowledge.

Good luck
Sam