[Hexagon] Remove unused declaration getModuleMatchQuality

getModuleMatchQuality was removed by:

  commit c3719c36
  Author: Daniel Dunbar <daniel@zuster.org>
  Date:   Sun Aug 2 23:37:13 2009 +0000

The Hexagon port was later added with getModuleMatchQuality by:

  commit 1213a7a5
  Author: Tony Linthicum <tlinth@codeaurora.org>
  Date:   Mon Dec 12 21:14:40 2011 +0000

While we are at it, this patch removes a reference to
getModuleMatchQuality in the documentation.