Remove unnecessary 'extern's.

Change-Id: Iba2b3fb6ff88e504f1657b915120ae43d58a1e03
diff --git a/libc/include/sys/personality.h b/libc/include/sys/personality.h
index 15a5e68..6f3a3c9 100644
--- a/libc/include/sys/personality.h
+++ b/libc/include/sys/personality.h
@@ -34,7 +34,7 @@
 
 __BEGIN_DECLS
 
-extern int personality(unsigned int persona) __INTRODUCED_IN(15);
+int personality(unsigned int persona) __INTRODUCED_IN(15);
 
 __END_DECLS