(cherry picked from commit 41597c28)

On file access LDBStore's tryAccessIdx() function created a faulty
GC Index Data entry, because not indexing the ikey correctly.
That caused the chunk addresses/hashes to start with '00' and the last
two digits were dropped. => Incorrect chunk address.

Besides the fix, the commit also contains a schema change which will
run the CleanGCIndex() function to clean the GC index from erroneous
entries.

Note: CleanGCIndex() rebuilds the index from scratch which can take
a really-really long time with a huge DB (possibly an hour).

Access count was not incremented when chunk was retrieved
from cache. So the garbage collector might have deleted the most
frequently accessed chunk from disk.
Co-authored-by: NFerenc Szabo <ferenc.szabo@ethereum.org>

* swarm: clean up unused private types and functions

Those that were identified by code inspection tool.

* swarm/storage: move/add Proximity GoDoc from deleted private function

The mentioned proximity() private function was deleted in:
1ca8fc1e6fa0ab4ab1aaca06d6fb32e173cd5f2f

Co-authored-by: NJanos Guljas <janos@resenje.org>
Co-authored-by: NBalint Gabor <balint.g@gmail.com>
Co-authored-by: NAnton Evangelatov <anton.evangelatov@gmail.com>
Co-authored-by: NViktor Trón <viktor.tron@gmail.com>

* swarm/storage: remove redundant increments for dataIdx and entryCnt

* swarm/storage: add Delete to LDBStore

* swarm/storage: wait for garbage collection

* swarm: propagate ctx, enable opentracing

* swarm/tracing: log error when tracing is misconfigured