~adigitoleo/nvim-plugins#5: [haunt.nvim] `require('haunt')` always defines user commands, which are documented as optional

Doing require('haunt') always defines the user commands, even though they are supposed to be optional.

The fix is to move the command definitions, which are already inside a (currently useless) conditional block, into the setup function body. Also, a second call to setup, whith define_commands = false should trigger command deletion.