Remove unnecessary 'extern's.

Change-Id: Iba2b3fb6ff88e504f1657b915120ae43d58a1e03
diff --git a/libc/include/sys/timerfd.h b/libc/include/sys/timerfd.h
index 0090233..a500060 100644
--- a/libc/include/sys/timerfd.h
+++ b/libc/include/sys/timerfd.h
@@ -42,10 +42,9 @@
 #define TFD_CLOEXEC O_CLOEXEC
 #define TFD_NONBLOCK O_NONBLOCK
 
-extern int timerfd_create(clockid_t, int) __INTRODUCED_IN(19);
-extern int timerfd_settime(int, int, const struct itimerspec*, struct itimerspec*)
-  __INTRODUCED_IN(19);
-extern int timerfd_gettime(int, struct itimerspec*) __INTRODUCED_IN(19);
+int timerfd_create(clockid_t, int) __INTRODUCED_IN(19);
+int timerfd_settime(int, int, const struct itimerspec*, struct itimerspec*) __INTRODUCED_IN(19);
+int timerfd_gettime(int, struct itimerspec*) __INTRODUCED_IN(19);
 
 __END_DECLS