xxs: RFR 8081780: JShell tool: Completion contains $REPL00DOESNOTMATTER

[ShinyaYoshida]

Hi Jan,
Please review this.

webrev:
http://cr.openjdk.java.net/~shinyafox/kulla/8081780/webrev.00/

bugs:
https://bugs.openjdk.java.net/browse/JDK-8081780

Regards,
shinyafox(Shinya Yoshida)