Remove Double.IsInfinity check from Math.Atan2
Remove Double.IsInfinity check from Math.Atan2

The coreclr S.P.CoreLIB do not have this
check and return -2.3561... for
this call like Math.Atan2(double.NegativeInfinity, double.NegativeInfinity)
but on CoreRT / N this return NaN because of this check.
This check has been there for ever , for reasons that
i don't know of.

shrah/corert,tijoytom/corert,shrah/corert,tijoytom/corert,yizhang82/corert,shrah/corert,gregkalapos/corert,yizhang82/corert,krytarowski/corert,krytarowski/corert,yizhang82/corert,gregkalapos/corert,tijoytom/corert,gregkalapos/corert,shrah/corert,krytarowski/corert,krytarowski/corert,gregkalapos/corert,tijoytom/corert,yizhang82/corert