Remove dependency from mini.comment

[raffaelemancuso]

Dependency from mini.comment should be removed.

Neovim has now builtin comment support.

[GCBallesteros]

The ability to define your own commenter plugins will be kept until nvim 0.12.0. What can be done now is remove the need to have one installed by defaulting to the builtin commenter if nvim >=0.10.0