Delete useless btrdiff.fish
It's a historical relic from back when the exozyme server still existed, but even if I ever still need to run that command, it's probably faster to just use btrbk diff directly instead of remembering how to use this convenience function
-function btrdiff -d "Get diff between last two btrfs snapshots"
- # Note: doing a btrfs balance will break this command
- run0 btrbk diff (printf %s\n /.snapshots/$argv[1].* | tail -n2) | less
-end