Removes icon key from job endpoint

What does this MR do?

When moving haml code into the new API we added the icon for deployment_status But we do not need it since we already have build.status in the response. Using the icon turns out to be more complicated for frontend since the build status is easier to parse.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [n.a.] Documentation created/updated
• [n.a.] Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [n.a.] Conforms to the database guides

#50904 (closed)

gitlab-org/gitlab-ce!21307 MR introducing the deployment_status key