Remove unused variables

Saw there were a few unused `require`'s when looking at utils.js and decided to do a quick pass and take out anything obviously unused (not unused arguments, except [where they're incorrect](https://github.com/tgriesser/node-postgres/compare/brianc:master...tgriesser:unused-vars?expand=1#diff-259dec4414a400a6e895f16ff1d0ca3bR111)).