MAINT: Removed unused member from risk class.

`runonce` is only ever written to, but never used.

zipline/finance/risk.py

@@ -317,7 +317,6 @@ class RiskMetricsBase(object):
                 x.date <= returns[-1].date
             ]
 
-        self.runonce = True
         self.algorithm_returns = self.mask_returns_to_period(returns)
         self.benchmark_returns = self.mask_returns_to_period(benchmark_returns)
         self.calculate_metrics()
@@ -342,7 +341,6 @@ class RiskMetricsBase(object):
                 end=self.end_date
             )
             raise Exception(message)
-        self.runonce = False
 
         self.num_trading_days = len(self.benchmark_returns)
         self.benchmark_volatility = self.calculate_volatility(