platforms: remove unused function

platforms/posix/src/main.cpp

@@ -596,11 +596,6 @@ bool is_already_running(int instance)
 	return false;
 }
 
-bool px4_exit_requested(void)
-{
-	return _exit_requested;
-}
-
 bool file_exists(const std::string &name)
 {
 	struct stat buffer;

src/platforms/px4_posix.h

@@ -136,8 +136,6 @@ __EXPORT const char 	*px4_get_topic_names(unsigned int *handle);
  */
 __EXPORT uint64_t	hrt_system_time(void);
 
-__EXPORT bool		px4_exit_requested(void);
-
 
 #endif