Enter, Merge, Switch, NextIteration, Exit

These were a mistake. IIUC one of the major changes for TF2 is control_flow_v2 3, where they switched these all to use a new implementation based on functions (PartitionedCall, StatefulPartitionedCall), so that downstream compilers have a chance to understand what the original code’s structure was.
Skye explains it in this TF-internals:
            

At some point the runtime does lower it to the old version for execution but my understanding was that TF2 doesn’t ever generate these into the graph anymore (does it? It’s explained in the video somewhere).
We never delete deprecated ops, so graphs containing these will continue to work.