LibJS: Remove infallibility marker from DefaultTimeZone invocation

This is an editorial change to the ECMA-402 spec. See:
https://github.com/tc39/ecma402/commit/46aa5cc

Also add an ECMA-402 spec link to the DefaultTimeZone implementation, as
that definition supersedes ECMA-262.

Userland/Libraries/LibJS/Runtime/Date.cpp

@@ -364,6 +364,7 @@ i64 get_named_time_zone_offset_nanoseconds(StringView time_zone_identifier, Cryp
 }
 
 // 21.4.1.10 DefaultTimeZone ( ), https://tc39.es/ecma262/#sec-defaulttimezone
+// 6.4.3 DefaultTimeZone ( ), https://tc39.es/ecma402/#sup-defaulttimezone
 StringView default_time_zone()
 {
     return TimeZone::current_time_zone();

Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp

@@ -216,7 +216,7 @@ ThrowCompletionOr<DateTimeFormat*> initialize_date_time_format(VM& vm, DateTimeF
 
     // 30. If timeZone is undefined, then
     if (time_zone_value.is_undefined()) {
-        // a. Set timeZone to ! DefaultTimeZone().
+        // a. Set timeZone to DefaultTimeZone().
         time_zone = default_time_zone();
     }
     // 31. Else,