Remove unused fields from JpaDistributionSet (#1704)

These fields also could lead to big memory usage if the JPA provider doesn't get LAZY hint

Signed-off-by: Marinov Avgustin <Avgustin.Marinov@bosch.com>

hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/DistributionSetFilter.java

@@ -28,6 +28,4 @@ public final class DistributionSetFilter {
     private final String searchText;
     private final Boolean selectDSWithNoTag;
     private final Collection<String> tagNames;
-    private final String assignedTargetId;
-    private final String installedTargetId;
 }