Simplify aten_unbind when shape is static #11040

Job	Run time
build_docs (ubuntu-latest)	3m 36s
build_docs (windows-latest)	5m 50s
update_readme	7s
test (ubuntu-latest, py311-onnx-weekly)	19m 16s
test (ubuntu-latest, py311)	18m 12s
test (ubuntu-latest, py312)	19m 14s
test (ubuntu-latest, py311-torch-nightly)	19m 36s
test (ubuntu-latest, py311-onnx-ir-git)	16m 27s
test (windows-latest, py312)	8m 18s
test (macos-latest, py312)	16m 44s
test (windows-latest, py311)	8m 32s
test (ubuntu-latest, py310)	18m 47s
test (macos-latest, py311-onnx-weekly)	15m 57s
test (macos-latest, py311)	11m 21s
test (macos-latest, py311-onnx-ir-git)	9m 6s
test (windows-latest, py311-onnx-weekly)	11m 18s
test (macos-latest, py311-ort-nightly)	18m 38s
test (ubuntu-latest, py311-ort-nightly)	18m 23s
test (windows-latest, py311-ort-nightly)	8m 56s
test (windows-latest, py311-torch-nightly)	10m 2s
test (macos-latest, py311-torch-nightly)	11m 45s
test (windows-latest, py311-onnx-ir-git)	9m 39s
test (windows-latest, py310)	7m 40s
test (macos-latest, py310)	8m 1s
	4h 55m 25s

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