Remove RootPageId mapping when queue entries are deleted.

[brianmadden]

https://github.com/brianmadden/krawler/blob/master/src/main/kotlin/io/thelandscape/krawler/crawler/Krawler.kt#L231

and

https://github.com/brianmadden/krawler/blob/master/src/main/kotlin/io/thelandscape/krawler/crawler/Krawler.kt#L219

Should be modified to remove root page mappings when any queue entries associated with them are removed from the queue.