Remove the merge manually message from MRs
This is an actionable insight from the [UX Department: MRs experience async critique](https://gitlab.com/gitlab-org/ux-research/-/issues/1073) research ([insight][insight]).
### What
In the merge request widget, below the **merge** section, the message `You can merge this merge request manually using the command line` is almost always displayed, even when merging is blocked or the current user doesn't have permissions.
Here are a few cases:
1. There are conflicts and the current user can't merge it locally:

1. The pipeline has failed and must succeed to be able to merge (from https://gitlab.com/gitlab-org/gitlab/-/issues/291168):

1. When unresolved threads must be resolved
1. When the MR is still in draft
1. When merge trains are enabled
1. And likely other cases where merge isn't possible
Additionally, given the [history of this message](https://gitlab.com/gitlab-org/gitlab/-/issues/291994#note_491935311), it doesn't seem to add value.
### How
Remove the merge manually message.
[insight]: https://dovetailapp.com/projects/14109fbc-dfdd-4204-a54e-9c80ba8b7bba/insights/77cf90af-b89d-4520-89a4-277684714da6
issue