isPrecompiled() needs to be updated to reflect byzantium

[axic]

See https://github.com/ethereumjs/ethereumjs-util/blob/master/index.js#L519, which limits it to address 0 to 5.

(This feature is used by the -vm and -accounts.)

[axic]

Update:

• apparently it is not used by accounts anymore for a while: Remove isPrecompiled and weird usage of isContract ethereumjs-account#2
• the VM does its check internally

This feature could be removed in the next breaking change, but for now it still needs to be updated.

[holgerd77]

Yes, removed this from the VM when working on Byzantium. Found this too implicit with too few benefits.