Prune vendor directory?

[carolynvs]

When I migrated us to dep, I didn't turn on pruning because of a gap in dep, and how it treats the code-generator repo that caused dep to no properly vendor the non-go code in that repo. Once golang/dep#1545 is merged however, we can turn pruning on if we like.

Do we want to?

[MHBauer]

Is pruning 'do not include packages we never call'? If so, why not?

[carolynvs]

There are three pruning options available:

• Unused packages - Remove packages that aren't imported
• Non-go code - Removes files not used by go
• Go tests - Removes *_test.go files

I'll submit a PR that demonstrates this, and my workaround for not having that dep PR merged yet. Should be able to remove quite a bit of cruft.