news: Tweak existing v3.3.0 entries

Some of the content was not following the (loosely established)
style, and some of the XML was not aligned properly.

docs/news.xml

@@ -39,7 +39,7 @@
     <section title="Improvements">
       <change>
         <summary>
-          The libvirt Hyper-V driver now supports Hyper-V 2012 and newer.
+          hyperv: Support Hyper-V 2012 and newer
         </summary>
         <description>
           Starting with Hyper-V 2012 the API has changed causing the existing
@@ -50,7 +50,7 @@
       </change>
       <change>
         <summary>
-          Add support for nested HVM domains in the libxl driver
+          libxl: Add support for nested HVM domains
         </summary>
         <description>
           Xen has supported nested HVM domains since version 4.4. The