Remove reference to internal issue tracker.
Remove reference to internal issue tracker.

As per comments from Adrian on GINCA pull request #5.

winksaville/common-tool,winksaville/common-tool,seL4/common-tool,hendersa/px4-common-tool,hendersa/px4-common-tool,hendersa/px4-common-tool,seL4/common-tool,winksaville/common-tool,seL4/common-tool