Remove track specific wording from triangle readme

[tgecho]

We had a confused user of the Elm track because elm-test does not have a "skip" concept (exercism/elm#66). It seems to me that this sort of instruction would be more suitable as a comment in the test file for now.

The other option might be just qualify this note a bit.

[Cohen-Carlisle]

👍

[petertseng]

And in fact any languages that do have skips are probably usingn that approach in all their exercises, which means it might best go somewhere global rather than per-exercise.

As just one example see how Ruby put their skip documentation into https://github.com/exercism/xruby/blob/master/docs/TESTS.md

So seems good to merge this!

[tgecho]

Thanks! 👍