CMakeProjectManager: Get rid of an unqualified friend

The latest libClang gives us following warning:

cmakebuildconfiguration.h:104:18: warning: unqualified friend
declaration referring to type outside of the nearest enclosing namespace
is a Microsoft extension; add a nested name specifier

Deleting is the right fix.

Change-Id: I4ccccf286044ca45ec78b0ea03a4ce8d979f06b4
Reviewed-by: hjk <hjk@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildconfiguration.h

@@ -101,7 +101,6 @@ private:
 
     friend class CMakeBuildSettingsWidget;
     friend class CMakeBuildSystem;
-    friend class CMakeProject;
 };
 
 class CMakeProjectImporter;