Remove legacy optimizer #9415

Job	Run time
test (ubuntu-latest, py312)	17m 7s
build_docs (ubuntu-latest)	2m 36s
update_readme	4s
test (ubuntu-latest, py311)	16m 42s
build_docs (windows-latest)	5m 50s
test (ubuntu-latest, py311-torch-nightly)	16m 20s
test (ubuntu-latest, py311-onnx-weekly)	16m 37s
test (ubuntu-latest, py311-ort-nightly)	3m 9s
test (ubuntu-latest, py310)	16m 59s
test (windows-latest, py312)	3m 46s
test (windows-latest, py311)	3m 34s
test (windows-latest, py311-torch-nightly)	8m 50s
test (windows-latest, py311-onnx-weekly)	3m 16s
test (windows-latest, py311-ort-nightly)	3m 37s
test (windows-latest, py310)	3m 49s
test (macos-latest, py312)	7m 19s
test (macos-latest, py311)	7m 33s
test (macos-latest, py311-torch-nightly)	9m 49s
test (macos-latest, py311-onnx-weekly)	8m 22s
test (macos-latest, py311-ort-nightly)	5m 36s
test (macos-latest, py310)	6m 48s
	2h 47m 43s

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