Remove duplicate declaration of mlock, munlock.

Bug: http://b/28067717
Change-Id: I4fe5a4368e5112a5d6aed5de9549155d3352962a
diff --git a/libc/include/sys/mman.h b/libc/include/sys/mman.h
index a19ceb5..170300a 100644
--- a/libc/include/sys/mman.h
+++ b/libc/include/sys/mman.h
@@ -65,13 +65,10 @@
 extern int munlockall(void);
 extern int mlock(const void*, size_t);
 extern int munlock(const void*, size_t);
-extern int madvise(void*, size_t, int);
-
-extern int mlock(const void*, size_t);
-extern int munlock(const void*, size_t);
 
 extern int mincore(void*, size_t, unsigned char*);
 
+extern int madvise(void*, size_t, int);
 extern int posix_madvise(void*, size_t, int);
 
 __END_DECLS