clavis,
You need to do the following –
1. Open MyEclipse IDE, from menu options click on Help > MyEclipse configuration Center
2. From My Software > Personal Software section, right click on – Subversive Integration for the M2Eclipse Project and click on [remove]
3. An alert shows up to confirm the removal. Click on [Yes]
4. Next right click on the update site under – My Software > Personal Software and click on [Delete]
The reason you see this is because M2Eclipse is already part of Maven4MyEclipse. In case you are planning to use subversive, I suggest you add Subversive Plug-in (w/related) using Quick-Add Popular Plug-ins.