defrag: proper cleanup of base of there are no entries in it.

NB! This is rather dangerous to do on the fly - extensive testing
needed.
stats: various counter fixes

This fixes double counting of 'records total' and counts removed entries
in opened base.
Also reset counters on cleanup.
blob: fixed log message
blob: removed unused parameter from eblob_cache_insert()
stats: removed hashed counter

We can't destinguish between cache update and insert easily, so remove
counter for now.

In future we can just run iterator against the tree in periodic thread to
count entries in l2hash collision/non-collision and hash trees.