input_common/sdl: Remove unused header includes and forward declarations

Gets rid of a few unnecessary inclusion dependencies. It also uncovered
a few indirect inclusion dependencies being relied upon.

src/input_common/sdl/sdl.h

@@ -6,15 +6,8 @@
 
 #include <memory>
 #include <vector>
-#include "core/frontend/input.h"
 #include "input_common/main.h"
 
-union SDL_Event;
-
-namespace Common {
-class ParamPackage;
-} // namespace Common
-
 namespace InputCommon::Polling {
 class DevicePoller;
 enum class DeviceType;

src/input_common/sdl/sdl_impl.cpp

@@ -6,7 +6,6 @@
 #include <atomic>
 #include <cmath>
 #include <functional>
-#include <iterator>
 #include <mutex>
 #include <string>
 #include <thread>
@@ -15,7 +14,6 @@
 #include <utility>
 #include <vector>
 #include <SDL.h>
-#include "common/assert.h"
 #include "common/logging/log.h"
 #include "common/math_util.h"
 #include "common/param_package.h"

src/input_common/sdl/sdl_impl.h

@@ -6,7 +6,10 @@
 
 #include <atomic>
 #include <memory>
+#include <mutex>
 #include <thread>
+#include <unordered_map>
+#include "common/common_types.h"
 #include "common/threadsafe_queue.h"
 #include "input_common/sdl/sdl.h"
 
@@ -16,9 +19,9 @@ using SDL_JoystickID = s32;
 
 namespace InputCommon::SDL {
 
-class SDLJoystick;
-class SDLButtonFactory;
 class SDLAnalogFactory;
+class SDLButtonFactory;
+class SDLJoystick;
 
 class SDLState : public State {
 public: