remove broken wiki link

The wiki contained minimal useful information for contributors to CBMC
(the wiki was largely administrative inforation aimed at Kroening's former
research group), and the link is dead now anyway.

Author: polgreen

README.md

@@ -3,8 +3,6 @@
 [![Build Status][coverity_img]][coverity]
 [![Build Status][codecov_img]][codecov]
 
-[CProver Wiki](http://www.cprover.org/wiki)
-
 [CProver Documentation](http://cprover.diffblue.com)
 
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