Now that WGPU has upgraded its dependency on `libloading`, we can
finally remove our fake `libloading` 0.7 crate! 🙌
I found this audit and review easiest to do by generating a diff. that
ignores whitespace-only differences. In my case, I did the following:
```
git diff --ignore-space-at-eol --ignore-space-change --ignore-all-space --ignore-blank-lines
```
Differential Revision: https://phabricator.services.mozilla.com/D209290
506602b6e6