Drop group_deploy_keys and group_deploy_keys_groups

What does this MR do and why?

Drop group_deploy_keys and group_deploy_keys_groups

This means we will drop the group_deploy_keys, group_deploy_keys_groups tables (and corresponding models) effectively. The GroupDeployKey feature is unfinished, and it is not exposed to any end user, so dropping the tables and classes should be safe to do so.

Pertains to #408933

Addresses #541118 (closed) && #567415 (closed)

Follows !204222 (merged)

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