Remove std::string alias (for real this time)

Also use std::string_view in a few more places.

src/libutil/logging.hh

@@ -216,6 +216,6 @@ inline void warn(const std::string & fs, const Args & ... args)
 
 void warnOnce(bool & haveWarned, const FormatOrString & fs);
 
-void writeToStderr(const string & s);
+void writeToStderr(std::string_view s);
 
 }