Remove FeeProvider

[rantan]

I propose to remove FeeProvider in next major release. So that, I want to make it to mark deprecated so far.

Current implementation of FeeProvider is dis-functionality to use below points.

• It uses fixed fee amount. It doesn't consider TXs size to decide fee amount. So, some TXs will face insufficient tapyrus amount to pay fee.
• UTXOProvider is usable to the same objective that is bear fee instead of sender's wallet. And it is able to provide adjusted amount of fee to TXs.