Remove 'return' statements that can never be reached

Clang -Wunreachable-code-return warns otherwise.

Source/CursesDialog/cmCursesOptionsWidget.cxx

@@ -59,7 +59,6 @@ bool cmCursesOptionsWidget::HandleInput(int& key, cmCursesMainForm*, WINDOW* w)
     {
     return false;
     }
-  return false;
 }
 
 void cmCursesOptionsWidget::AddOption(std::string const & option )

Source/cmSystemTools.cxx

@@ -1662,7 +1662,6 @@ long copy_data(struct archive *ar, struct archive *aw)
       return (r);
       }
     }
-  return r;
 }
 
 bool extract_tar(const char* outFileName, bool verbose,