Fix bug in metadata updating when deleting SLs in the admin.
Fix bug in metadata updating when deleting SLs in the admin.

For https://unisubs.sifterapp.com/projects/12298/issues/558430/comments

ujdhesa/unisubs,pculture/unisubs,ujdhesa/unisubs,norayr/unisubs,wevoice/wesub,ujdhesa/unisubs,norayr/unisubs,ReachingOut/unisubs,norayr/unisubs,ReachingOut/unisubs,eloquence/unisubs,ofer43211/unisubs,wevoice/wesub,wevoice/wesub,pculture/unisubs,eloquence/unisubs,eloquence/unisubs,norayr/unisubs,eloquence/unisubs,ReachingOut/unisubs,ujdhesa/unisubs,ofer43211/unisubs,ofer43211/unisubs,pculture/unisubs,wevoice/wesub,pculture/unisubs,ReachingOut/unisubs,ofer43211/unisubs