Remove dead code remains of WinDIB usage

This used to have meaning for Windows 9x support via SDL 1.2; the issue
described in README was never mentioned in the context of SDL2.

Add missing include to video header while we're at it.

README

@@ -248,18 +248,6 @@ KEYBOARD: I can't type \ or : in DOSBox.
     "enter" and "L".
 
 
-KEYBOARD: Right Shift and "\" doesn't work in DOSBox. (Windows only)
-    This may happen if Windows thinks that you have more than one keyboard
-    connected to your PC when you use some remote control devices.
-    To verity this problem run cmd.exe, navigate to DOSBox program folder
-    and type:
-    set sdl_videodriver=windib
-    dosbox.exe
-    check whether keyboard started to work properly. As windib is slower it is
-    best to use one of the two solutions provided here:
-    https://www.vogons.org/viewtopic.php?t=24072
-
-
 KEYBOARD: The keyboard lags.
     Lower the priority setting in the DOSBox configuration file, for example
     set "priority=normal,normal". You might also want to try lowering the

include/video.h

@@ -16,10 +16,11 @@
  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  */
 
-
 #ifndef DOSBOX_VIDEO_H
 #define DOSBOX_VIDEO_H
 
+#include "types.h"
+
 #define REDUCE_JOYSTICK_POLLING
 
 typedef enum {
@@ -68,10 +69,6 @@ void GFX_EndUpdate( const Bit16u *changedLines );
 void GFX_GetSize(int &width, int &height, bool &fullscreen);
 void GFX_LosingFocus(void);
 
-#if defined (WIN32)
-bool GFX_SDLUsingWinDIB(void);
-#endif
-
 #if defined (REDUCE_JOYSTICK_POLLING)
 void MAPPER_UpdateJoysticks(void);
 #endif

src/gui/sdlmain.cpp

@@ -308,7 +308,6 @@ struct SDL_Block {
 	SDL_Rect updateRects[1024];
 	Bitu num_joysticks;
 #if defined (WIN32)
-	bool using_windib;
 	// Time when sdl regains focus (alt-tab) in windowed mode
 	Bit32u focus_ticks;
 #endif