[split] Move peco plugin to oh-my-fish/plugin-peco

https://github.com/oh-my-fish/plugin-peco

plugins/peco/README.md

-peco
-----
-
-Based directly on the percol plugin.
-
-Please bind peco_select_history to your favorite key.
-
-If you'd like to bind CTRL+R
-```
-function fish_user_key_bindings
-  bind \cr 'peco_select_history (commandline -b)'
-end
-```

plugins/peco/peco_select_history.fish

-function peco_select_history
-  if test (count $argv) = 0
-    set peco_flags --layout=bottom-up
-  else
-    set peco_flags --layout=bottom-up --query "$argv"
-  end
-
-  history|peco $peco_flags|read foo
-
-  if [ $foo ]
-    commandline $foo
-  else
-    commandline ''
-  end
-end