MSBuild Task syntax for deleting files

You can delete the files in those directories first and then the dir itself with

<Target Name="SomeTarget">
    <ItemGroup>
        <FilesToDelete Include="Path\To\Obj\**\*"/>
    </ItemGroup>   
    <Delete Files="@(FilesToDelete)" />   
    <RemoveDir Directories="Path\To\Obj\" />
</Target>