Fix #6319: [Win32] don't use clipping; draw whole screen every frame

When we clip the region that is only been redrawn, something
weird happens on Windows. When pushing 60 frames per second on a
60Hz monitor, it appears that the clipped region is often shown
of another frame, instead of the current.

Examples of this are:
- pause the game, move your mouse to the left, and at the right
  speed it totally disappears.
- fast aircrafts seem to be in several places at once, weirdly
  lagging behind.
- in title screen, moving your mouse gives you the idea it is
  jumping places, instead of smooth movements.

In the end, if you do nothing, everything is correct, so it is
eventually consistent. Just when we are firing many BitBlt in
a clipped region, the in-between is not.

What goes wrong exactly, I honestly do not know. On every frame
that we push to the DC is a mouse painted, but visually it
sometimes appears like it is not. Recording with external software
shows it really is there.
It is also not our eyes playing tricks on us, as the first example
makes it really clear the mouse pointer really is not painted.

And to be clear, with the mouse this is easiest reproduceable,
as high-speed objects are influences by this most. But this happens
for all movement that redraws small regions.

Either way, not using clipped regions resolves the issue completely,
and there appears to be little to no penalty (I failed to measure
any impact of drawing the full screen). So better have a good game
than fast code, I guess?

src/video/win32_v.cpp

@@ -334,19 +334,9 @@ void VideoDriver_Win32::Paint()
 
 	if (IsEmptyRect(_dirty_rect)) return;
 
-	/* Convert update region from logical to device coordinates. */
-	POINT pt = {0, 0};
-	ClientToScreen(_wnd.main_wnd, &pt);
-
-	RECT r = { _dirty_rect.left, _dirty_rect.top, _dirty_rect.right, _dirty_rect.bottom };
-	OffsetRect(&r, pt.x, pt.y);
-
-	/* Create a device context that is clipped to the region we need to draw.
-	 * GetDCEx 'consumes' the update region, so we may not destroy it ourself. */
-	HRGN rgn = CreateRectRgnIndirect(&r);
-	HDC dc = GetDCEx(_wnd.main_wnd, rgn, DCX_CLIPSIBLINGS | DCX_CLIPCHILDREN | DCX_INTERSECTRGN);
-
+	HDC dc = GetDC(_wnd.main_wnd);
 	HDC dc2 = CreateCompatibleDC(dc);
+
 	HBITMAP old_bmp = (HBITMAP)SelectObject(dc2, _wnd.dib_sect);
 	HPALETTE old_palette = SelectPalette(dc, _wnd.gdi_palette, FALSE);