Don't make Done button blue

It is a little much to make a ordinary close button of an
informative dialog blue. Just leave it gray.

src/gnome-software.ui

@@ -1030,9 +1030,6 @@
                 <property name="visible">True</property>
                 <property name="can_focus">True</property>
                 <property name="receives_default">True</property>
-                <style>
-                  <class name="suggested-action"/>
-                </style>
               </object>
               <packing>
                 <property name="expand">False</property>