Revert [dynamo] support group=None when rewriting collectives (#12018) (#120677)
This reverts commit 298c686d3f7bc26399481b8830e71c4f02ce629c.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120677
Approved by: https://github.com/yifuwang, https://github.com/huydhn
