[lua] Tango with a Tracker Quest Bug Fix

[slashtangent]

I affirm:

• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
• I understand I should leave resolving conversations to the LandSandBoat team so that reviewers won't miss what was said.
• I have read and understood the Contributing Guide and the Code of Conduct.
• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Removes the quest complete check from the quest.
Tango isn't repeatable so it was causing a loop where the player would get another KI for Tango.

Steps to test these changes

!addmission 6 818
!completemission 6 818
!addmission 6 828
Talk to Despachiaire to get KI Letter from Shikaree X
!zone <Boneyard Gully>
Enter battlefield
Win. -- Quest Complete
Talk to Despachiaire again who won't give you another letter from Shikaree X