Missing functionality: type_check_cons_in, type_check_cons_union

[eksperimental]

I'm using Gradualizer via Gradient and I get the following warnings

===> Compiling gradualizer
src/gradualizer.erl:45:2: Warning: opaque type top() is underspecified and therefore meaningless

src/typechecker.erl:3234:1: Warning: function type_check_cons_in/4 is unused
src/typechecker.erl:3247:1: Warning: function type_check_cons_union/4 is unused
src/typechecker.erl:4612:1: Warning: function verbose/3 is unused
src/typechecker.erl:4870:1: Warning: function gen_partition/3 is unused
src/typechecker.erl:4872:1: Warning: function paux/3 is unused

[erszcz]

type_check_cons_in and type_check_cons_union seem to implement some typing rules which were never finished - the code is there, but it's neither exported nor called. We can remove those, bet let's keep this issue not to forget about these missing typing rules.