Remove placeholder text from application details label.

This placeholder text can show if GNOME Software takes time to load the
appropriate information e.g. when running with --local-filename

src/gnome-software.ui

@@ -197,7 +197,6 @@
                 <child>
                   <object class="GtkLabel" id="application_details_header">
                     <property name="can_focus">False</property>
-                    <property name="label">GNU Image Manipulation Program</property>
                     <property name="selectable">False</property>
                     <property name="ellipsize">end</property>
                     <style>