Remove legacy code, bump version number

Full changes list:

* Don't check ECDSA signatures for PoW blocks ever, with exception for the first 9689 blocks;
* Remove ECDSA signing related code from mining RPC APIs;
* Trim leading zeros from the hex representation of trust score in the block dump functions;
* Don't check lk_max_locks if compiled with USE_LEVELDB flag;
* Add hash and stake modifier checkpoints for block #44200.