Remove duplicate executions in intervention list

Input: hosts = HostA, HostB, new date = some new date

Job: Postpone Interventions

Result: 2 new interventions get scheduled for just 1 intervention that needs to be postponed

This happens because the executions list contains duplicate interventions. The intervention list originally does not have duplicates but the duplicates are introduced while filtering the executions as per the hosts or some other parameter.

The proposed fix is to remove the duplicates from the execution list.