Remove unnecessary 'extern's.

Change-Id: Iba2b3fb6ff88e504f1657b915120ae43d58a1e03
diff --git a/libc/include/sys/wait.h b/libc/include/sys/wait.h
index e0afabc..90eb35b 100644
--- a/libc/include/sys/wait.h
+++ b/libc/include/sys/wait.h
@@ -49,9 +49,9 @@
 #define W_EXITCODE(ret, sig)    ((ret) << 8 | (sig))
 #define W_STOPCODE(sig)         ((sig) << 8 | 0x7f)
 
-extern pid_t  wait(int *);
-extern pid_t  waitpid(pid_t, int *, int);
-extern pid_t wait4(pid_t, int*, int, struct rusage*) __INTRODUCED_IN(18);
+pid_t wait(int*);
+pid_t waitpid(pid_t, int*, int);
+pid_t wait4(pid_t, int*, int, struct rusage*) __INTRODUCED_IN(18);
 
 /* Posix states that idtype_t should be an enumeration type, but
  * the kernel headers define P_ALL, P_PID and P_PGID as constant macros
@@ -59,7 +59,7 @@
  */
 typedef int idtype_t;
 
-extern int  waitid(idtype_t which, id_t id, siginfo_t *info, int options);
+int waitid(idtype_t which, id_t id, siginfo_t* info, int options);
 
 __END_DECLS