Remove unneeded sorts

As we need to start using the --trump option in `tidy_mappings.pl`,
we must preserve sort order until that point. `tidy_mappings.pl` sorts
the output for us.
More descriptive name for fold-mappings.rb
Reverse fetched CSVs to preserve "newer is better"

We now reverse the fetch CSV file so that we can keep the existing
"newer is better" ordering mentality for the moment.