applet: Move common IsRunning underlying variable to the Applet class

Gets rid of basic duplication.

src/core/hle/applets/erreula.h

@@ -17,18 +17,12 @@ public:
     ResultCode ReceiveParameter(const Service::APT::MessageParameter& parameter) override;
     ResultCode StartImpl(const Service::APT::AppletStartupParameter& parameter) override;
     void Update() override;
-    bool IsRunning() const override {
-        return started;
-    }
 
+private:
     /// This SharedMemory will be created when we receive the LibAppJustStarted message.
     /// It holds the framebuffer info retrieved by the application with
     /// GSPGPU::ImportDisplayCaptureInfo
     Kernel::SharedPtr<Kernel::SharedMemory> framebuffer_memory;
-
-private:
-    /// Whether this applet is currently running instead of the host application or not.
-    bool started = false;
 };
 
 } // namespace Applets