Removing wildcard imports kind of stalled out.

[cbiffle]

After achieving consensus with the team, in #1752 I started removing uses of wildcard imports (that is, use somecrate::*;) in Hubris. I'm using Clippy to try to avoid regressions in the areas where they've been removed.

But there's a lot of Hubris left, and new wildcard imports are occasionally still added (potentially by copy-paste from previous ones).

It would be nice to clean the rest of this up, and it would be nice to spread the work across more people than just me.

[aapoalas]

I'm interested in doing more of these mechanical cleanups, if that is considered permissible. #1857 removes the rest of userlib::* imports.