[NLL] Loss of `'static` relaxation suggestion under NLL

[jackh726]

In the src/test/ui/suggestions/impl-on-dyn-trait-with-implicit-static-bound.rs test, we give the suggestion consider relaxing the implicit `'static` requirement under migrate mode. Under NLL, we lose that suggestion, and have a slightly less user-friendly error message.

Importantly, with the suggestion, the code is rustfix-able. Without the suggestion, it is not.

[b-naber]

@jackh726 Is this a blocker for removing migrate mode?

[jackh726]

In my opinion, no. It's just a suggestion.