Remove ocp:spawn* functions or move them to the separate library

[hauleth]

I could count on the fingers of the one had all situations when I have used raw spawn, in almost all situations I have encountered it was better to use any kind of gen_* modules or one of the many Elixir utilities over raw spawn. As you cannot use it with built ins, I would suggest that we either remove them, as these are trivial to implement, or move them to separate library, so we could remove needless code from the main tree.