Similar to rsync repo delay deletes for rrdp repos to after processing

Similar to rsync repo delay deletes for rrdp repos to after processing
all files. Now RRDP has a weak sync mechanism and therefor not all
unreferenced files can be removed, instead look at the list of removes
which were part of the delta processing and remove those files.
Warn and keep the file if a delta specifies to remove a file which is
actually still referenced.
OK benno@