Drop Arrays.parallelStream()?

[Brian Goetz]

We dropped the parallel versions of all the static generator/factory 
methods in Streams a while ago, in favor of just letting people do (say) 
IntStream.range(...).parallel().  Since then, we have also greatly 
reduce the runtime cost of Stream.parallel().

We still have the separate .parallelStream() method on Collection and in 
the static methods in Arrays.

I still really like Collection.parallelStream; it has huge 
discoverability advantages, and offers a pretty big return on API 
surface area -- one more method, but provides value in a lot of places, 
since Collection will be a really common case of a stream source.

Arrays are in a middle ground.  We have eight Arrays.stream() methods 
and eight Arrays.parallelStream() methods (four types, both whole-array 
and slice versions).  I'm having a bit of a YAGNI twinge for the 
Arrays.parallelStream forms, and could see ditching them.  (The 
implementations are trivial and small, so that is not an argument to 
ditch them -- we should make this decision purely on API considerations.)

If we did this, Collection would have the sole parallelStream method; 
everything else would have to go through .parallel().  Which seems fine 
to me.