remove duplicate math.pyi

builtins/2and3/math.pyi

@@ -31,6 +31,7 @@ def fsum(iterable: Iterable) -> float: ...
 def gamma(x: float) -> float: ...
 def hypot(x: float, y: float) -> float: ...
 def isinf(x: float) -> bool: ...
+def isfinite(x: float) -> bool: ...
 def isnan(x: float) -> bool: ...
 def ldexp(x: float, i: int) -> float: ...
 def lgamma(x: float) -> float: ...