remove time query from tx burst now

[guruofquality]

The transmit time is recorded in the burst now (aka without a timestamp). The purpose is to store it for the end of burst time to simulate waiting for the end of burst acknowledgement. The problem being that this imposes an extra readback wait to read the tx time, a wait that we otherwise dont need in most cases. Consider testing without the time read and changing the implementation.

   //pack the metadata
    if (not _inTxBurst)
    {
        md.flags |= BLADERF_META_FLAG_TX_BURST_START;
        if ((flags & SOAPY_SDR_HAS_TIME) != 0)
        {
            md.timestamp = _timeNsToTxTicks(timeNs);
        }
        else
        {
            md.flags |= BLADERF_META_FLAG_TX_NOW;
            bladerf_get_timestamp(_dev, BLADERF_MODULE_TX, &md.timestamp);
        }
        _txNextTicks = md.timestamp;
    }