C4Application: Remove Win32 window focus hack

It is not a good idea and can let Clonk hang if the current foreground windodw
is not processing messages.

See https://devblogs.microsoft.com/oldnewthing/20130619-00/?p=4043.

src/C4Application.cpp

@@ -628,30 +628,6 @@ void C4Application::OnCommand(const char *szCmd)
 	}
 }
 
-void C4Application::Activate()
-{
-#ifdef _WIN32
-	// Activate the application to regain focus if it has been lost during loading.
-	// As this is officially not possible any more in new versions of Windows
-	// (BringWindowTopTop alone won't have any effect if the calling process is
-	// not in the foreground itself), we are using an ugly OS hack.
-	DWORD nForeThread = GetWindowThreadProcessId(GetForegroundWindow(), 0);
-	DWORD nAppThread = GetCurrentThreadId();
-	if (nForeThread != nAppThread)
-	{
-		AttachThreadInput(nForeThread, nAppThread, TRUE);
-		BringWindowToTop(FullScreen.hWindow);
-		ShowWindow(FullScreen.hWindow, SW_SHOW);
-		AttachThreadInput(nForeThread, nAppThread, FALSE);
-	}
-	else
-	{
-		BringWindowToTop(FullScreen.hWindow);
-		ShowWindow(FullScreen.hWindow, SW_SHOW);
-	}
-#endif
-}
-
 void C4Application::SetNextMission(const char *szMissionFilename)
 {
 	// set next mission if any is desired

src/C4Application.h

@@ -139,7 +139,6 @@ class C4Application : public CStdApp
 public:
 	virtual void Quit() override;
 	void QuitGame(); // quit game only, but restart application if in fullscreen startup menu mode
-	void Activate(); // activate app to gain full focus in OS
 	void SetNextMission(const char *szMissionFilename);
 };
 

src/C4StartupMainDlg.cpp

@@ -304,8 +304,6 @@ void C4StartupMainDlg::OnShown()
 	// First show
 	if (fFirstShown)
 	{
-		// Activate the application (trying to prevent flickering half-focus in win32...)
-		Application.Activate();
 		// Set the focus to the start button (we might still not have the focus after the update-check sometimes... :/)
 		SetFocus(pStartButton, false);
 	}