request #7593: Prevent from deleting a tracker if used in AD

Change-Id: If41ca110ecaf9feff5f5ed5e463d2a25646d20ca
Merge commit 'refs/changes/71/3171/8' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  request #7593: Prevent from deleting a tracker if used in AD

Change-Id: I274f2e919d361624be2762eac70a4490441dc450
This is Tuleap 7.6.99.44

Change-Id: I23502abf12d3f516320de1e21d52484f321ff228