RFR(xs): 8245970: IntStream.html#reduce doc should not mention average

[Conor Cleary]

Hi,

The method-level documentation of Intstream::reduce(int, 
IntBinaryOperator) mentions the average function as a case of reduction 
even though the function cannot be used with the reduce method. This 
might cause confusion, this fix therefore removes the mention of the 
average function from the @apiNote.

bug: https://bugs.openjdk.java.net/browse/JDK-8245970
webrev: http://cr.openjdk.java.net/~jboes/ccleary/webrevs/8242281/webrev.00/

Regards,
Conor