Don't export "hum" date versions for trade objects.

They are not used and have a rather high performance penalty due to
using arrow.get

tests/rpc/test_rpc_telegram.py

@@ -177,9 +177,7 @@ def test_telegram_status(default_conf, update, mocker) -> None:
             'pair': 'ETH/BTC',
             'base_currency': 'BTC',
             'open_date': arrow.utcnow(),
-            'open_date_hum': arrow.utcnow().humanize,
             'close_date': None,
-            'close_date_hum': None,
             'open_rate': 1.099e-05,
             'close_rate': None,
             'current_rate': 1.098e-05,