You could just use string.Replace:
string str = "\"The best time to start is now. Some time gen-\r\n"
+"erally means no time. You can put away as much as I put away, if you try.\"\r\n"
+"\" All right, I’ll do it—next week.\"\r\n"
+"\" No, this week,\" and Dale smiled good-hu-\r\n"
+"moredly.\r\n"
+"\"Gracious, Dale! are you becoming my guar-\r\n"
+"dian.\"\r\n";
str = str.Replace("-\r\n", "-");
Console.WriteLine(str);
"The best time to start is now. Some time gen-erally means no time. You can put away as much as I put away, if you try."
" All right, I’ll do it—next week."
" No, this week," and Dale smiled good-hu-moredly.
"Gracious, Dale! are you becoming my guar-dian."