Removed leading underscore in structure names

Fixes https://github.com/libsdl-org/SDL/issues/6856
Closes https://github.com/libsdl-org/SDL/pull/6914
Closes https://github.com/libsdl-org/SDL/pull/6915
Closes https://github.com/libsdl-org/SDL/pull/6916
Closes https://github.com/libsdl-org/SDL/pull/6917
Closes https://github.com/libsdl-org/SDL/pull/6918
Closes https://github.com/libsdl-org/SDL/pull/6919

include/SDL3/SDL_audio.h

@@ -925,8 +925,8 @@ extern DECLSPEC int SDLCALL SDL_ConvertAudio(SDL_AudioCVT * cvt);
     - You push data as you have it, and pull it when you need it
  */
 /* this is opaque to the outside world. */
-struct _SDL_AudioStream;
-typedef struct _SDL_AudioStream SDL_AudioStream;
+struct SDL_AudioStream;
+typedef struct SDL_AudioStream SDL_AudioStream;
 
 /**
  * Create a new audio stream.

include/SDL3/SDL_haptic.h

@@ -137,8 +137,8 @@ extern "C" {
  *  \sa SDL_HapticOpenFromJoystick
  *  \sa SDL_HapticClose
  */
-struct _SDL_Haptic;
-typedef struct _SDL_Haptic SDL_Haptic;
+struct SDL_Haptic;
+typedef struct SDL_Haptic SDL_Haptic;
 
 
 /**

include/SDL3/SDL_sensor.h

@@ -48,8 +48,8 @@ extern "C" {
  *  for sensors, and load appropriate drivers.
  */
 
-struct _SDL_Sensor;
-typedef struct _SDL_Sensor SDL_Sensor;
+struct SDL_Sensor;
+typedef struct SDL_Sensor SDL_Sensor;
 
 /**
  * This is a unique ID for a sensor for the time it is connected to the system,