RFR: 8227231: JDWP help information shows use of obsolete Xdebug flag

[Daniil Titov]

Please review a small fix [1] that removes references to obsolete XDebug flag from JDWP help returned by "java -Xrunjdwp:help" command.
A new CSR [2] was created for these changes and needs to be reviewed.

[1] Webrev: http://cr.openjdk.java.net/~dtitov/8227231/webrev.01/ 
[2] CSR: https://bugs.openjdk.java.net/browse/JDK-8232075 
[3] Issue: https://bugs.openjdk.java.net/browse/JDK-8227231 

Thank you,
Daniil