Remove reference to mirrors in index.html files

There are places where references to mirror sites should be kept in like
in the FAQ (currently FAQ 6.2 with the title 'May I mirror the IOCCC
website?' and with the named anchor 'mirrors', 'website_mirrors' and
'website_mirroring').

2013/README.md

@@ -12,10 +12,6 @@ Some ANSI C compilers are not quite as good as they should be.  If
 yours is lacking, you may need to compile using gcc instead of your
 local compiler.
 
-The IOCCC has a website and now has a number of international mirrors.
-The primary website can be found at [www.ioccc.org](https://www.ioccc.org).
-
-
 
 ## Remarks on some of the entries
 

2013/index.html

@@ -401,8 +401,6 @@ the Author’s remarks for even more details.</p>
 <p>Some ANSI C compilers are not quite as good as they should be. If
 yours is lacking, you may need to compile using gcc instead of your
 local compiler.</p>
-<p>The IOCCC has a website and now has a number of international mirrors.
-The primary website can be found at <a href="https://www.ioccc.org">www.ioccc.org</a>.</p>
 <h2 id="remarks-on-some-of-the-entries">Remarks on some of the entries</h2>
 <p>We believe you will again be impressed with this year’s winning entries.</p>
 <p>This year, 9 won 15 awards. For the first time in the history of the contest,