[Hexagon] Remove unused declaration getModuleMatchQuality

getModuleMatchQuality was removed by:

  commit c3719c3
  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 1213a7a
  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.

llvm/docs/WritingAnLLVMBackend.rst

@@ -216,7 +216,6 @@ simply return a class member.
       return &InstrInfo.getRegisterInfo();
     }
     virtual const DataLayout *getDataLayout() const { return &DataLayout; }
-    static unsigned getModuleMatchQuality(const Module &M);
 
     // Pass Pipeline Configuration
     virtual bool addInstSelector(PassManagerBase &PM, bool Fast);

llvm/lib/Target/Hexagon/HexagonTargetMachine.h

@@ -36,8 +36,6 @@ class HexagonTargetMachine : public LLVMTargetMachine {
   ~HexagonTargetMachine() override;
   const HexagonSubtarget *getSubtargetImpl(const Function &F) const override;
 
-  static unsigned getModuleMatchQuality(const Module &M);
-
   void registerPassBuilderCallbacks(PassBuilder &PB) override;
   TargetPassConfig *createPassConfig(PassManagerBase &PM) override;
   TargetTransformInfo getTargetTransformInfo(const Function &F) const override;