Revert "Add dataframe parameter to custom_stoploss() and custom_sell() methods."

This reverts commit 595b8735f8.

# Conflicts:
#	freqtrade/optimize/backtesting.py
#	freqtrade/strategy/interface.py

tests/strategy/test_default_strategy.py

@@ -41,5 +41,4 @@ def test_default_strategy(result, fee):
                                        rate=20000, time_in_force='gtc', sell_reason='roi') is True
 
     assert strategy.custom_stoploss(pair='ETH/BTC', trade=trade, current_time=datetime.now(),
-                                    current_rate=20_000, current_profit=0.05, dataframe=None
-                                    ) == strategy.stoploss
+                                    current_rate=20_000, current_profit=0.05) == strategy.stoploss