General coding practices improvement in ZetaClient

[lumtis]

Describe the Issue

Contains some tasks that can be addresses in the same PR for general code practices improvement in ZetaClient

• Remove all commented code if not used without context
  • Example Bitcoin PostGasPrice: commented logger code
• Leave empty line between components of a functions
  • Example Bitcoin PostGasPrice: empty lines after error handling
• There are public and private methods in random orders, we should put public first and private methods after
  • Example in bitcoin_client
  • tss/tss_signer
• All function/variable comments should start with the name
  • Example: BtcOutTxBytesDeposit and other vars in bitcoin/fee
  • The constant definitions in evm
• Remove unused variables, unless for a specific reason specific in comment
  • Example: different variable in config_chain.go
• Use empty lines between every functions
  • Example in evm_client
• Find and remove all unused functions
  • BuildReceiptsMap in evm_client