Remove the temporary util.promisify dependency

[Raynos]

This util.promisify dependency increases the number of transitive dependencies of xml2js from 3 total => 27 total.

I inlined the implementation for the one place it was being used so that the xml2js library has a low dependency and will install fast.

I manually tested this change on node 12,10,8,6,4 and 0.12

[coveralls]

Coverage increased (+0.03%) to 97.727% when pulling 3c2c99a on optoolco:reduce-deps into aefc64a on Leonidas-from-XIV:master.

[Leonidas-from-XIV]

Hmm, that's interesting. I am surprised that you can use reject & friends in such old Node versions but the code looks good, passes CI and having fewer dependencies is neat for sure. Thanks for your contribution, merging!

[Raynos]

Only node 0.10 does not have global.Promise available ; it's also missing other apis like EventEmitter.prototype.removeAllListeners that causes the tests to fail.

Thanks for merging the contribution, let me know once you've released a new version :)

( git checkout master && npm version patch && git push origin master --tags && npm publish )

I'm excited about having a version of aws-sdk with less dependencies.

[Leonidas-from-XIV]

Just pushed 0.4.23.