LibJS: Use new format functions everywhere

This changes the remaining uses of the following functions across LibJS:

- String::format() => String::formatted()
- dbg() => dbgln()
- printf() => out(), outln()
- fprintf() => warnln()

I also removed the relevant 'LogStream& operator<<' overloads as they're
not needed anymore.

Libraries/LibJS/Runtime/Reference.h

@@ -98,6 +98,4 @@ private:
     bool m_global_variable { false };
 };
 
-const LogStream& operator<<(const LogStream&, const Value&);
-
 }