clean-up the 'FileLink -> EntityLink change'

EntityLink table: reorder fields in index to allow existing searches use it.

getFilesOfEntity: make join condition of index fields
commitUnlinkEntitiesByParent: new DB func
commitDeleteObject: separate unlink query to multiple to make SQL indices work.
commitResetObject: idem
getFileLinks, releaseFiles: remove deprecated comment

amplifyCell: get back to use getFileLinks API call
renderFile: idem
destroyIPv4Prefix: get back to use releaseFiles API call
destroyIPv6Prefix: idem
commitDeleteVS: idem
commitDeleteRSPool: idem
commitDeleteVSG: idem