Removed declarations of removed functions.

src/internal.h

@@ -264,8 +264,6 @@ void _glfwPlatformTerminate(void);
 const char* _glfwPlatformGetVersionString(void);
 
 // Input mode support
-void _glfwPlatformEnableSystemKeys(_GLFWwindow* window);
-void _glfwPlatformDisableSystemKeys(_GLFWwindow* window);
 void _glfwPlatformSetCursorPos(_GLFWwindow* window, int x, int y);
 void _glfwPlatformSetCursorMode(_GLFWwindow* window, int mode);