Eliminate dependency on frame-metadata

[JoshOrndorff]

Followup to #82

Now that paritytech/substrate#14398 landed in Substrate, we should be able to remove frame-metadata, the last frame-specific logic from our dependency tree.

This is a pretty small change, we just need to do the corresponding Substrate update (probably next monthly release) and we will magically get the smaller dependency graph.

[muraca]

@JoshOrndorff up for visibility 😄

[JoshOrndorff]

Solved in #86