Schedule the removal of a redundant index on lfs_objects_projects

What does this MR do and why?

This change is to schedule the removal of idx_lfs_objects_projects_on_project_id_lfs_object_id_repo_type from lfs_objects_projects

An excerpt from \d+ lfs_objects_projects

"idx_lfs_objects_projects_on_project_id_lfs_object_id_repo_type" UNIQUE, btree (project_id, lfs_object_id, repository_type)
"lfs_objects_projects_on_project_id_lfs_object_id_null_repo_type" UNIQUE, btree (project_id, lfs_object_id) WHERE repository_type IS NULL
"lfs_objects_projects_on_project_id_lfs_object_id_with_repo_type" UNIQUE, btree (project_id, lfs_object_id, repository_type) WHERE repository_type IS NOT NULL

More context from a previous MR: !179613 (merged)

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Related to #467119 (closed)