Modify operation enum.

Remove ROTATED_BBOX_TRANSFORM since it is no longer needed.
Add DETECTION_POSTPROCESS for SSD NMS postprocessing op.

Bug: 120983926
Test: NeuralNetworksTest_static
Change-Id: Id6b1021c8707734499feddddf0aac24a3fff90f8
Merged-In: Id6b1021c8707734499feddddf0aac24a3fff90f8
(cherry picked from commit 1f59bc3b)