update `SequentialLR` signature (#69817)
Summary:
- ~optimizer isn't required for `SequentialLR` since it's already present in the schedulers. Trying to match the signature of it with `ChainedScheduler`.~
- ~`verbose` isn't really used anywhere so removed it.~
updated missing docs and added a small check
Pull Request resolved: https://github.com/pytorch/pytorch/pull/69817
Reviewed By: ngimel
Differential Revision: D33069589
Pulled By: albanD
fbshipit-source-id: f015105a35a2ca39fe94c70acdfd55cdf5601419
