Revert "Update aosp/master libcxx rebase to r263688"

The world is burning.

This reverts commit c004fd909c, reversing
changes made to 1418e4163d.

utils/sym_check/sym_diff.py

@@ -1,16 +1,7 @@
 #!/usr/bin/env python
-#===----------------------------------------------------------------------===##
-#
-#                     The LLVM Compiler Infrastructure
-#
-# This file is dual licensed under the MIT and the University of Illinois Open
-# Source Licenses. See LICENSE.TXT for details.
-#
-#===----------------------------------------------------------------------===##
 """
 sym_diff - Compare two symbol lists and output the differences.
 """
-
 from argparse import ArgumentParser
 import sys
 from sym_check import diff, util