Revert "Merch.Race.MapGen.Measure: Correct distance generation in the presence of loops."

This reverts commit 1045537836f2bb0731fccdc0e3305a44b8eca7d8.

  This isn't actually necessary due to how the algorithm works.
    Since covered hexes are already considered, we don't actually
    need to consider covered settlements.
Merch.Race.CMerch: Modify behavior of computer merchants.