Remove ProjectFileFactory::canOpen, it's not defined anywhere

Change-Id: I82bcf2d1e83427ff11672d7e93c1ce27e4afc979
Reviewed-by: Daniel Teske <daniel.teske@digia.com>

src/plugins/projectexplorer/pluginfilefactory.h

@@ -49,7 +49,6 @@ class ProjectFileFactory : public Core::IDocumentFactory
 
 public:
     virtual QStringList mimeTypes() const;
-    bool canOpen(const QString &fileName);
     Core::Id id() const;
     QString displayName() const;