[rnn/gru] no batch dim (#70442)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/60585
TODO:
* [x] Doc updates
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70442
Reviewed By: zou3519
Differential Revision: D33460427
Pulled By: jbschlosser
fbshipit-source-id: c64d9624c305d90570c79d11a28557f9ec667b27
