SchemeShard: data erasure refactoring

[lex007in]

There are some problems with the current implementation:

1. Unwanted logic in the SetPartitioning() method (DataShard and SchemeShard: handle borrowed parts in data erasure #15451 (comment))
2. Cleanup is not guaranteed in case of tablet deletion (SchemeShard can receive a TEvDeleteTabletReply from the hive before the tablet data is GC'd).