Updating class names, and using existing utility classes.

Removes extra btn class from dropdown

Closes #60224

See merge request gitlab-org/gitlab-ce!27160

Deletes unused CSS
Moves prometheus selectors into a prometheus file

In the deployments page, the links inside a
dropdown had an extra btn class

Use plain job name in the "Deploy to..." dropdown
Both in the old haml template and in the new vue component

Ensure a vue.js component to confirm the re-deployment/rollback of an
environment pops up when rollback/re-deploy has been clicked so the user
must confirm their actions before accidentally rolling back or
re-deploying an environment.

Only on the `environment-table` view.

The soft-archived builds cannot be run after some deadline time.
The intent is to aggressively recycle old builds after sometime.

Signed-off-by: Tao Wang <twang2218@gmail.com>