Auto merge of #9132 - hellow554:maybe_trait_bound_on_type_repetition, r=Manishearth

Maybe trait bound on type repetition

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changelog: fix maybe trait on [`type_repetition_in_bounds`] lint

I simplified the two for loops, which did exactly the same. Only downside is, that I need a `copied`, but that's to convert from `&&` to `&`, to that should be a noop?

One more thing: I only handle [`TraitBoundModifier::Maybe`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/enum.TraitBoundModifier.html#variant.Maybe). Can anyone give me an example (and testcase) for [`TraitBoundModifier::MaybeConst`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/enum.TraitBoundModifier.html#variant.MaybeConst)?

closes #8770