Deleting a Decision Table 
The delete option is only available for those decision tables created in the rules manager. You cannot delete a decision table :
After you upload the changes made to the decision table.
If it is being used in a rule. More Information: Using a Decision Table in a Rule.
Procedure
In the Rules Navigator view, expand the project node and select the ruleset or flow ruleset.
The ruleset or flow ruleset overview page opens in the editor window.
Under the Decision Tables section, select the decision table.
Choose the Delete button.
In the dialog box that appears, choose OK.