Remove conditional checks for the internal ID tables

The following discussion from gitlab-ce!27544 should be addressed:

• @abrandl started a discussion: (+1 comment)

  There are two other instances that follow the same pattern:

  • app/models/user_interacted_project.rb
  • app/models/project_ci_cd_setting.rb

  We should probably also fix those in a similar fashion once this MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27544 is accepted.