Remove incorrect code from contract details decoder

[djkelleher]

Problem - The current contract details decoder contains a bit of code that should only be used in the bond contract details decoder.

Effect - The function first correctly assigns the timeZoneId, but then later in the function body overwrites it with the timezone TWS is set to use.

Solution - Delete the extra code.

For reference, here is the logic from the official API from Interactive Brokers:

def readLastTradeDate(self, fields, contract: ContractDetails, isBond: bool):
        lastTradeDateOrContractMonth = decode(str, fields)
        if lastTradeDateOrContractMonth is not None:
            if '-' in lastTradeDateOrContractMonth: 
                splitted = lastTradeDateOrContractMonth.split('-')
            else:
                splitted = lastTradeDateOrContractMonth.split()

            if len(splitted) > 0:
                if isBond:
                    contract.maturity = splitted[0]
                else:
                    contract.contract.lastTradeDateOrContractMonth = splitted[0]

            if len(splitted) > 1:
                contract.lastTradeTime = splitted[1]

            if isBond and len(splitted) > 2:
                contract.timeZoneId = splitted[2]