Moved keys_sorted_by_value() to tkgui/parametersframe (the only place it's used), and removed values_sorted_by_key() (which has remained unused for almost 2 years).
Moved keys_sorted_by_value() to tkgui/parametersframe (the only place it's used), and removed values_sorted_by_key() (which has remained unused for almost 2 years).

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