Remove sys and freelist modules in v4.0.0

[thefourtheye]

As both sys and freelist are deprecated, 4.0.0 might be a good release to remove them.

[Fishrock123]

Probably not in reality, unless we know for sure almost nothing depends on them. See: #1704 and probably cc @chrisdickinson

[targos]

Also, sys and freelist are not properly deprecated on node 0.12. It will be an abrupt change if they disappear from the converged release.

[thefourtheye]

@targos Oh yeah. Then this should be done in 5.0.0 only then 😢