graph.py implements safe_remove_nodes incorrectly

[TomWildenhain-Microsoft]

Describe the bug
Edge case where nodes A, B, C have dependencies A->B->C and safe_remove_nodes is called on set {A, B}. A is removed despite being unsafe to delete.

Urgency
Not urgent

[guschmue]

There should not be a safe_remove_nodes() ever since if something points into the nodes to be removed - they be rewired by the caller because only the caller knows what to do with those.