[InstCombine] Remove CreateNonTerminatorUnreachable (NFC)

The function was introduced without a use on Jun 3, 2020 in commit
2a6c871.  Note that the identical
function is defined in InstCombineInternal.h without static, which is
in use.

Author: kazutakahirata

llvm/include/llvm/Transforms/InstCombine/InstCombiner.h

@@ -361,14 +361,6 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner {
     return ConstantVector::get(Out);
   }
 
-  /// Create and insert the idiom we use to indicate a block is unreachable
-  /// without having to rewrite the CFG from within InstCombine.
-  static void CreateNonTerminatorUnreachable(Instruction *InsertAt) {
-    auto &Ctx = InsertAt->getContext();
-    new StoreInst(ConstantInt::getTrue(Ctx),
-                  UndefValue::get(Type::getInt1PtrTy(Ctx)), InsertAt);
-  }
-
   void addToWorklist(Instruction *I) { Worklist.push(I); }
 
   AssumptionCache &getAssumptionCache() const { return AC; }