Remove clippy workflow.

[thejpster]

The code is auto-generated - we couldn't fix the clippy warnings even if we wanted to.

Although ... now we've pinned clippy in #19, this isn't strictly required.

Thoughts?

[jannic]

I'm unsure. You are right that we can't (easily) fix clippy errors. And the current checks are only semi valuable, because doing the clippy checks with an old rust version totally ignores that we already have several clippy warning when using a current rust version.
But then, I would want to know if some svd2rust update introduced new clippy issues. So the clippy job isn't useless. And, assuming that the number of updates on this repo stays low, the cost of having that additional CI job is small.