Remove temp index group membership namespace id

Merged Serena Fang requested to merge remove-tmp-idx-group-membership-namespace-id into master

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#353538 (closed)

Related to !78715 (merged) (merged). We added a temporary index for batched background migration, we can remove this index when migration is done.

Once !93240 (merged) is merged, we can rebase and merge this. !93324 (comment 1073556082)

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Edited by Serena Fang