Task identity links not updated when deleting candidates

[JacekMiszczak]

Describe the bug
When the candidates of a task are modified, specifically deleted by calling org.flowable.task.service.delegate.DelegateTask#deleteCandidateUser, the list of identity links in the task object is not updated. What's worse, that persists through different task listeners.

Expected behavior
After calling org.flowable.task.service.delegate.DelegateTask#deleteCandidateUser I expect that org.flowable.task.service.delegate.DelegateTask#getCandidates will reflect the changes.

Code
org.flowable.task.service.delegate.DelegateTask#deleteCandidateUser
org.flowable.task.service.delegate.DelegateTask#getCandidates
org.flowable.task.service.impl.persistence.entity.TaskEntityImpl#getIdentityLinks

Additional context
Flowable version 7.1.0.27

[JacekMiszczak]

I've created a pull request with a proposed solution: #3998