Fix request #5751 : PUT /milestones/123/content does not remove anymore links from other trackers than content trackers.

Change-Id: I011f37731c6580b9c2bad35678eb393507a04b73
Merge commit 'refs/changes/01/1601/2' of http://gerrit.tuleap.net/tuleap into tuleap-stable-master

* http://gerrit.tuleap.net/tuleap:
  Fix request #5751 : PUT /milestones/123/content does not remove anymore links from other trackers than content trackers.

Change-Id: I1fb34d5c7b7ebcd3ae53710ce4ded099c0bfeb1c
Tuleap 6.8.99.18

Change-Id: I56d3f28410d4f5ecf1b2da7f6a371ef47659a5ed