remove InteractiveUtils.dumptype (#42093)

It was broken (`TypeName.abstract`) is not defined anymore, so clearly has
no users nor tests and can simply be deleted at this point.

Author: vtjnash

stdlib/InteractiveUtils/src/InteractiveUtils.jl

@@ -279,74 +279,6 @@ function supertypes(T::Type)
     return S === T ? (T,) : (T, supertypes(S)...)
 end
 
-# dumptype is for displaying abstract type hierarchies,
-# based on Jameson Nash's typetree.jl in https://github.com/JuliaArchive/Examples
-function dumptype(io::IO, @nospecialize(x), n::Int, indent)
-    print(io, x)
-    n == 0 && return  # too deeply nested
-    isa(x, DataType) && x.name.abstract && dumpsubtypes(io, x, Main, n, indent)
-    nothing
-end
-
-directsubtype(a::DataType, b::DataType) = supertype(a).name === b.name
-directsubtype(a::UnionAll, b::DataType) = directsubtype(a.body, b)
-directsubtype(a::Union, b::DataType) = directsubtype(a.a, b) || directsubtype(a.b, b)
-# Fallback to handle TypeVar's
-directsubtype(a, b::DataType) = false
-function dumpsubtypes(io::IO, x::DataType, m::Module, n::Int, indent)
-    for s in names(m, all = true)
-        if isdefined(m, s) && !isdeprecated(m, s)
-            t = getfield(m, s)
-            if t === x || t === m
-                continue
-            elseif isa(t, Module) && nameof(t) === s && parentmodule(t) === m
-                # recurse into primary module bindings
-                dumpsubtypes(io, x, t, n, indent)
-            elseif isa(t, UnionAll) && directsubtype(t::UnionAll, x)
-                dt = unwrap_unionall(t)
-                println(io)
-                if isa(dt, DataType) && dt.name.wrapper === t
-                    # primary type binding
-                    print(io, indent, "  ")
-                    dumptype(io, dt, n - 1, string(indent, "  "))
-                else
-                    # aliases to types
-                    print(io, indent, "  ", m, ".", s, "{")
-                    tvar_io::IOContext = io
-                    tp = t
-                    while true
-                        show(tvar_io, tp.var)
-                        tvar_io = IOContext(tvar_io, :unionall_env => tp.var)
-                        tp = tp.body
-                        if isa(tp, UnionAll)
-                            print(io, ", ")
-                        else
-                            print(io, "} = ")
-                            break
-                        end
-                    end
-                    show(tvar_io, tp)
-                end
-            elseif isa(t, Union) && directsubtype(t::Union, x)
-                println(io)
-                print(io, indent, "  ", m, ".", s, " = ", t)
-            elseif isa(t, DataType) && directsubtype(t::DataType, x)
-                println(io)
-                if t.name.module !== m || t.name.name != s
-                    # aliases to types
-                    print(io, indent, "  ", m, ".", s, " = ")
-                    show(io, t)
-                else
-                    # primary type binding
-                    print(io, indent, "  ")
-                    dumptype(io, t, n - 1, string(indent, "  "))
-                end
-            end
-        end
-    end
-    nothing
-end
-
 # TODO: @deprecate peakflops to LinearAlgebra
 export peakflops
 """