Remove unnecessary filtering of blank cache records in webcrawler and patent metadata retriever

[przemyslawjacewicz]

Ticket #1221 will remove writing of empty records to webcrawler and patent metadata retriever caches. We should also remove already existing empty records in caches to avoid their propagation to next caches. The removal is implemented as a filter on RDD read from cache. The filter will be unnecessary after first IIS run after closing #1221 so we should remove it.