code: func (db *schemaUpdater) updateSchemaTo5() {
  	t := db.newReadWriteTransaction()
  	var nk []byte
  	for _, folderStr := range db.ListFolders() {
  		nk = db.keyer.GenerateNeedFileKey(nk, []byte(folderStr), nil)
  		t.deleteKeyPrefix(nk[:keyPrefixLen+keyFolderLen])
  	}
  	t.close()
  
  	db.updateSchema2to3()
  }
docs: // updateSchemaTo5 resets the need bucket due to bugs existing in the v0.14.49
  // release candidates (dbVersion 3 and 4)
  // https://github.com/syncthing/syncthing/issues/5007
  // https://github.com/syncthing/syncthing/issues/5053