Consider dropping the dkms completion

[Emil Velikov <emil.l.velikov@xxxxxxxxx>]

Greetings team,

Since dkms v3.0.13[1], the zsh completion has been imported in the
upstream project.

We have already started clearing and updating it, and plan to do so in
the foreseeable future. With that in mind, I think it makes sense to
drop the ones from zsh itself.
Massive thanks to everyone who contributed and maintained it over the years.

Thanks
Emil
[1] https://github.com/dell/dkms/releases/tag/v3.0.13