CPlusPlus, Utils: Move namespace icon from CPlusPlus to Utils

...so that it can be used in the ScxmlEditor plugin

Change-Id: I0e0ed050f7765bcc901db3bb2c3273456a228b5e
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/libs/cplusplus/Icons.cpp

@@ -215,7 +215,7 @@ QIcon Icons::iconForType(IconType type)
     }
     case NamespaceIconType: {
         const static QIcon icon(Icon({
-            {QLatin1String(":/codemodel/images/namespace.png"), Theme::IconsCodeModelKeywordColor}
+            {QLatin1String(":/utils/images/namespace.png"), Theme::IconsCodeModelKeywordColor}
         }, Icon::Tint).icon());
         return icon;
     }

src/libs/cplusplus/cplusplus.qrc

@@ -8,8 +8,6 @@
         <file>images/keyword@2x.png</file>
         <file>images/macro.png</file>
         <file>images/macro@2x.png</file>
-        <file>images/namespace.png</file>
-        <file>images/namespace@2x.png</file>
         <file>images/signal.png</file>
         <file>images/signal@2x.png</file>
         <file>images/slot.png</file>