Remove two unused `extern`s on function declarations.

These were the only two in our headers.

Change-Id: Iaa3dd5ff8e95130d6fea39c68518f72d634aaa5c
diff --git a/libc/include/bits/fortify/socket.h b/libc/include/bits/fortify/socket.h
index 02f94cc..1c3605b 100644
--- a/libc/include/bits/fortify/socket.h
+++ b/libc/include/bits/fortify/socket.h
@@ -30,8 +30,7 @@
 #error "Never include this file directly; instead, include <sys/socket.h>"
 #endif
 
-extern ssize_t __sendto_chk(int, const void* _Nonnull, size_t, size_t, int, const struct sockaddr* _Nullable,
-        socklen_t) __INTRODUCED_IN(26);
+ssize_t __sendto_chk(int, const void* _Nonnull, size_t, size_t, int, const struct sockaddr* _Nullable, socklen_t) __INTRODUCED_IN(26);
 ssize_t __recvfrom_chk(int, void* _Nullable, size_t, size_t, int, struct sockaddr* _Nullable, socklen_t* _Nullable);
 
 #if defined(__BIONIC_FORTIFY)