Remove __INTRODUCED_IN for obsolete API levels.

The NDK only supports >= 16, so remove anything older than that to avoid
giving the misleading impression that such old targets are still
supported.

(This change doesn't touch <unistd.h>. I'll follow up with that once the
outstanding FORTIFY changes to that file are in.)

Test: builds
Change-Id: I6cc6ecdb99fe228a4afa71f78e5fd45309ba9786
diff --git a/libc/include/sys/stat.h b/libc/include/sys/stat.h
index 84a5015..79113b6 100644
--- a/libc/include/sys/stat.h
+++ b/libc/include/sys/stat.h
@@ -185,8 +185,7 @@
 
 #define UTIME_NOW  ((1L << 30) - 1L)
 #define UTIME_OMIT ((1L << 30) - 2L)
-int utimensat(int __dir_fd, const char* __path, const struct timespec __times[2], int __flags)
-  __INTRODUCED_IN(12);
+int utimensat(int __dir_fd, const char* __path, const struct timespec __times[2], int __flags);
 int futimens(int __dir_fd, const struct timespec __times[2]) __INTRODUCED_IN(19);
 
 __END_DECLS