fix: Remove versions from local dev-dependencies

[Swatinem]

This way, cargo will not verify the versions when publishing, removing
the need to use cargo-hack for publishing.

fixes #374

[relaxolotl]

the changes look good, but it looks like CI isn't happy with this right now 😞

i don't see anything in the diff that deliberately tries to fix the problem with circular imports that you mentioned in the linked issue - will that be a problem once this is merged in?

[Swatinem]

The code coverage CI job is broken right now, its optional anyway.

The actual fix here is that cargo > 1.40 will ignore path-only dev-dependencies when publishing, thus we don’t need cargo-hack anymore. (Before, cargo would reject the release, because it checks that dev-dependencies actually exist on crates.io before publishing, which they don’t in case of circular deps)