Remove unnecessary attention mask
This PR is stale because it has been open for 14 days with no activity. Remove stale label or comment or update or this will be closed in 7 days. This PR is stale because it has been open for 14 days with no activity. Remove stale label or comment or update or this will be closed in 7 days. jenkins
# What does this PR do ?

Remove unnecessary attention masks. [Related MCore MR is here.](https://gitlab-master.nvidia.com/ADLR/megatron-lm/-/merge_requests/1259)