Revert "Fixed relative mode mouse events stopping if you click on the title bar"

This has been better fixed by b28ed02 or another related relative mouse mode change of @slouken in SDL 2.0.17 and as such can be reverted to reduce unneeded processing in WM_MOUSEMOVE

src/video/windows/SDL_windowsevents.c

@@ -773,9 +773,6 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
                         SDL_SendMouseMotion(data->window, 0, 0, center_x, center_y);
                     }
                 }
-            } else {
-                /* We still need to update focus */
-                SDL_SetMouseFocus(data->window);
             }
         }
         /* don't break here, fall through to check the wParam like the button presses */