Fixed missing etag condition in DB query.
After refactoring the code to enable clustering in 2.4, some of the DB queries for updating / deleting the presentity records were missing the etag condition. As a result you may have experienced records leaking in DB or strange errors about unique key violation.
Many thanks for helping with the troubleshooting to Dan Pascu @ AG Projects and to Ognjen Šešlija.
(cherry picked from commit 1ac9010f4fb8fff513ce25e06fdf210412c4a39b)