win_toolchain: remove old 7z binary

This was used back in the VS2010/VS2013 Express era, when we used it to
automatically extract bits and pieces from the publically available isos
for non-Pro users. Now we just require a Community Edition install so
this is unnecessary and unused.

Change-Id: I35bbb0ef29c940db128bd1fd4862d3d26e4cc002
Reviewed-on: https://chromium-review.googlesource.com/621783Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>

win_toolchain/7z/LICENSE

-  7-Zip
-  ~~~~~
-  License for use and distribution
-  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-  7-Zip Copyright (C) 1999-2012 Igor Pavlov.
-
-  Licenses for files are:
-
-    1) 7z.dll: GNU LGPL + unRAR restriction
-    2) All other files:  GNU LGPL
-
-  The GNU LGPL + unRAR restriction means that you must follow both 
-  GNU LGPL rules and unRAR restriction rules.
-
-
-  Note: 
-    You can use 7-Zip on any computer, including a computer in a commercial 
-    organization. You don't need to register or pay for 7-Zip.
-
-
-  GNU LGPL information
-  --------------------
-
-    This library is free software; you can redistribute it and/or
-    modify it under the terms of the GNU Lesser General Public
-    License as published by the Free Software Foundation; either
-    version 2.1 of the License, or (at your option) any later version.
-
-    This library is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-    Lesser General Public License for more details.
-
-    You can receive a copy of the GNU Lesser General Public License from 
-    http://www.gnu.org/
-
-
-  unRAR restriction
-  -----------------
-
-    The decompression engine for RAR archives was developed using source 
-    code of unRAR program.
-    All copyrights to original unRAR code are owned by Alexander Roshal.
-
-    The license for original unRAR code has the following restriction:
-
-      The unRAR sources cannot be used to re-create the RAR compression algorithm, 
-      which is proprietary. Distribution of modified unRAR sources in separate form 
-      or as a part of other software is permitted, provided that it is clearly
-      stated in the documentation and source comments that the code may
-      not be used to develop a RAR (WinRAR) compatible archiver.
-
-
-  --
-  Igor Pavlov
-