Relation memberships not handled correctly for ways segment deleting

[Daeron]

This patch makes the deleteWaySegment to just modify circular ways when a segment is deleted and not split the way at the first/last node, which is in practice always not what the user wanted.

[stoecker]

(In [2296]) see #3703 - patch by Daeron - deleting way segment cleanup

[Gubaer]

Run a couple of tests.

• Delete the middle segment from a way with three segments which belongs to a relation. Expected: the relation should still have the same member with the same role refering to the same way. In addition it should have a new member in adjacent position to the original member pointing to a new way (which is created because the way is split) and having the same role as the original members. Result: Looks fine.

• Delete the unique segment from a way with exactly one segment which belongs to a relation. Expected: this should delete the way and the member should be removed from the relation.
  JOSM displays a confirmation dialog to remove the way from the relation, as expected. If confirmed, the way is deleted and removed from the relation. Result: Looks fine.

Closing as worksforme.