TxEventQinOracleDB: Teardown script should clean up environment variables

[pasimoes]

The teardown script should clean the environment variables created by the workshop.

[pasimoes]

I decided to add a note after the clean-up script to inform the required "reconnect" in Cloud Shell to unset workshop environment variables.

echo
echo "Your shell was cleaned up!"
echo "All workshop-related configurations were removed from your .bashrc"
echo "But your environment variables are still present thus it is important to close this Cloud Shell section before any other use."
echo