Remove spurious reference to other exercise in linked-list metadata

[kytrinyx]

Copied from exercism/exercism#1440 reported by @patbl

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Maybe "simple-linked-list" was left out of the JavaScript track by accident? Here are the instructions for Linked List:

In simple-linked-list we created a push-down stack using a purely
functional linked list, but if we allow mutability and add another
pointer we can build a very fast deque data structure (Double-Ended
queue).

[...]

Under the hood we'll use the same Element class from
simple-linked-list, but there should be a @next and @prev attributes
that are both writable. @prev should point to the previous Element in
the list.