Update wildfly-elytron/tool README to not include info about github issues for tool

wildfly-elytron/tool used to be a separate repository that contained the code for the Elytron Tool. That repository also had it's own issue system, via Github issues.
Now that all that code is in the wildfly-elytron repository in the tool folder, we just use Jira to track the issues for elytron tool. 

The information in the README in the tool folder that indicates that issue tracking is being done through Github needs to be removed and instead needs to be specified is done here on JIRA.

https://github.com/wildfly-security/wildfly-elytron/tree/1.x/tool