Remove internal header inclusion guards

Inclusion of internal headers is already both centralized and follows
strict rules.  Inclusion guards are both an unneccessary maintenance
burden and may hide inclusion order bugs.

src/cocoa_joystick.h

@@ -24,9 +24,6 @@
 //
 //========================================================================
 
-#ifndef _glfw3_cocoa_joystick_h_
-#define _glfw3_cocoa_joystick_h_
-
 #include <IOKit/IOKitLib.h>
 #include <IOKit/IOCFPlugIn.h>
 #include <IOKit/hid/IOHIDLib.h>
@@ -50,4 +47,3 @@ typedef struct _GLFWjoystickNS
 void _glfwInitJoysticksNS(void);
 void _glfwTerminateJoysticksNS(void);
 
-#endif // _glfw3_cocoa_joystick_h_