If you wish to delete an entire Qos Metric from the database the the only supported method is to use the SLM portlet in UMP.
the below steps will guide you through this procsess

Release:
Component: UIMDEG

First add SLM portlet to your UMP if not already added

1. open UMP
2. Click Add - Page in the liferay tool bar, name the page SLM
3. Select the new SLM page and then click Add - Portlet in liferay bar
4. search for slm and click add

When you next open the SLM page it will contain the slm portlet

Now you are ready to delete the desired metric

1. Open SLM portlet and select "Quality Of Service" on the left hand side
2. Use the drop down to select order by probe
3. Locate the probe and dbl click
4. locate the desired qos , click the drop down and select delete
5. Confirm the deleteion