remove obsolete sentence

Doc/library/math.rst

@@ -347,10 +347,7 @@ Constants
    error-reporting behavior from the platform C implementation.  As a result,
    the specific exceptions raised in error cases (and even whether some
    arguments are considered to be exceptional at all) are not defined in any
-   useful cross-platform or cross-release way.  For example, whether
-   ``math.log(0)`` returns ``-Inf`` or raises :exc:`ValueError` or
-   :exc:`OverflowError` isn't defined, and in cases where ``math.log(0)`` raises
-   :exc:`OverflowError`, ``math.log(0L)`` may raise :exc:`ValueError` instead.
+   useful cross-platform or cross-release way.
 
    All functions return a quiet *NaN* if at least one of the args is *NaN*.
    Signaling *NaN*\s raise an exception. The exception type still depends on the