Traffic light removal is inconsistent

[ceeac]

To reproduce:

• Build a 4-way road intersection
• Build a traffic light onto the intersection
• Remove either the north-south or the east-west way across the intersection using the "Remove roads" tool
• Notice that, depending on whether the traffic light is red or green in that direction, the traffic light is removed or not

IMO the traffic light should be removed if the way is no longer an intersection (i.e. not a three- or fourway ribi) regardless of the state of the traffic light.

[prissi]

The traffic ligh should stay until there is at least a double straight ribi ... Investigating.

[prissi]

r10416 hopefully fixes this

[ceeac]

Seems to work fine now. I have added one additional test for this in r10420.

[prissi]

Thank you.