[vector] RFR -- removing Shape as type parameter

[Brian Goetz]

> I have only one comment: on API level S_Max_BIT overlaps with 
> Vector.preferredSpecies(), so it was agreed to not to expose it on API 
> level when [Int|...]MaxVector's were incorporated. With your change it 
> becomes part of the API:
>
> +public enum Shape {
> +    S_64_BIT(64),
> +    S_128_BIT(128),
> +    S_256_BIT(256),
> +    S_512_BIT(512),
> +    S_Max_BIT(Unsafe.getUnsafe().getMaxVectorSize(byte.class) * 8);
>
> -    static final SMaxBit S_Max_BIT = new SMaxBit();
> -    static final class SMaxBit extends Vector.Shape {
>
> I don't have a strong preference here: preferredSpecies() looks more 
> flexible, but I see that S_Max_BIT can be more convenient to use. My 
> point is: only one should stay.

Yes, I agree -- I want to address this in a subsequent round, but am 
trying to break things up into small, manageable changes.  Overall I 
think there's room to narrow the impact of Species on the API, but let's 
take that one step at a time.