Revert "Ensure that UTF-8 works if LANG contains it."

This was a really stupid change that I should have tested more
before pushing. It broke any non-interactive usage, such as SSH,
fish config, or parsing the script output, as config.fish is
loaded for everything.

There are no issues with different terminal emulators, so this
change will be pushed in the future, but only running in interactive
mode. I apologize for any issues caused by this commit.

This reverts commit d61adfbc532e856242730e198e492a2845754a91.