code: def unindex_layer(self, layer_id, use_cache=False):
      
  
      from hypermap.aggregator.models import Layer
      layer = Layer.objects.get(id=layer_id)
  
      if use_cache:
          LOGGER.debug('Caching layer with id %s for being removed from search engine' % layer.id)
          deleted_layers = cache.get('deleted_layers')
          if deleted_layers is None:
              deleted_layers = set([layer.id])
          else:
              deleted_layers.add(layer.id)
          cache.set('deleted_layers', deleted_layers)
          return
  
      if SEARCH_TYPE == 'solr':
          from hypermap.aggregator.solr import SolrHypermap
          LOGGER.debug('Removing layer %s from solr' % layer.id)
          try:
              solrobject = SolrHypermap()
              solrobject.remove_layer(layer.uuid)
          except Exception:
              LOGGER.error('Layer NOT correctly removed from Solr')
      elif SEARCH_TYPE == 'elasticsearch':
          # TODO implement me
          pass
docs: Remove the index for a layer in the search backend.
      If cache is set, append it to the list of removed layers, if it isn't send the transaction right away.