Remove unused Development EM roles

Why is this change being made?

Removing two Development Department EM manager roles, these should have been removed as part of Consolidate Development Department Engineering ... (!288 - merged)

I think as part of a rebase, the files had been edited elsewhere and were added back in. The intention of the previous MR was to remove and replace with https://handbook.gitlab.com/job-families/engineering/development/management/engineering-manager/, this MR completes that change.

There are already have redirects (aliases) in place for these from the previous MR https://gitlab.com/gitlab-com/content-sites/handbook/-/blob/pcalder-cleanup-manager-files/content/job-families/engineering/development/management/engineering-manager.md?plain=1#L3

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