[SourceKit] Remove option to regions reused as part of incremental parsing

unittests/SourceKit/SwiftLang/EditingTest.cpp

@@ -93,11 +93,6 @@ private:
     return SyntaxTreeTransferMode::Off;
   }
 
-  bool syntaxReuseInfoEnabled() override { return false; }
-
-  void
-  handleSyntaxReuseRegions(std::vector<SourceFileRange> ReuseRegions) override {
-  }
 };
 
 struct DocUpdateMutexState {