`Union` prints with duplicate elements, like `Union{Array, Memory, Memory}`

[nsajko]

Bisected to PR #57357 (20162ea):

$ ./julia-c6805e2c70/bin/julia -E 'Union{Array, Memory}'
Union{Array, Memory}
$ ./julia-20162ea394/bin/julia -E 'Union{Array, Memory}'
Union{Array, Memory, Memory}

[mbauman]

Looks like the typealias printing code is finding both Core.Memory and Base.Memory when it goes to show_unionaliases

julia> Base.make_typealiases(Union{Array, Memory})
(Core.SimpleVector[svec(:(Core.Memory), svec(T), Memory, (1, -1)), svec(:(Base.Memory), svec(T), Memory, (1, -1))], Memory)

[vtjnash]

Looks like an implementation mistake in #57357 so this should have a trivial fix.