Remove isc__tls_setfatalmode() function and the calls

With _exit() instead of exit() in place, we don't need
isc__tls_setfatalmode() mechanism as the atexit() calls will not be
executed including OpenSSL atexit hooks.

bin/confgen/util.c

@@ -47,6 +47,5 @@ fatal(const char *format, ...) {
 	vfprintf(stderr, format, args);
 	va_end(args);
 	fprintf(stderr, "\n");
-	isc__tls_setfatalmode();
 	_exit(EXIT_FAILURE);
 }