Blockchain: remove old fee calc logic

[jeffro256]

Reduce code and binary size by removing unused code paths related to fee calculations.

[hyc]

Is it really totally unused, or just unused in the current hardfork version? Do nodes need to use this code when verifying blocks from the earlier part of the blockchain?

[jeffro256]

The only location that Blockchain::check_fee() is called is in tx_memory_pool::add_tx(), and only for txs which are not "kept by block" (i.e. only called for ephemeral mempool validation and not for chain validation):

monero/src/cryptonote_core/tx_pool.cpp

Line 211 in 1bec712

if (!kept_by_block && !m_blockchain.check_fee(tx_weight, fee))

You can verify this yourself with git grep check_fee.