We used to have mutt alternative, provided by neomutt.
However, from commit edb9bbd0f3, ("neomutt: update to 20171013.",
2017-10-17) neomutt is no longger mutt.
Drop this alternative, so users can have better autocomplete,
let's say by: man 5 mutt<tab> and we can have simpler template.
Signed-off-by: Doan Tran Cong Danh <congdanhqx@gmail.com>