GitLab

Summary:
Various fixes for Masked LM

- use --activation-fn instead of --gelu
- use --dataset-impl instead of --lazy-load
- add embed_scale option to TransformerSentenceEncoder
- fix encoder_normalize_before to include a final layer norm
- delete BertLayerNorm
Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/573

Reviewed By: borguz

Differential Revision: D15317933

Pulled By: myleott

fbshipit-source-id: 8ecb46556ad43e76e92d41ed8f5a62e8516fd375