Consider refactoring external dependencies

[aaronsteers]

At this point we have rewritten much of the python libraries and in many cases have used alternative approaches such as new classes and metadata operations. We recently ran into a bug with a nested dependency, and a simple fix is to remove the reference to this library.

Related to:

• Refactor "Singer interop" helpers to a public singer-sdk.singer module #208

[aaronsteers]

@tayloramurphy - We're still having some bugs/issues related to the datetime library. I've asked @edgarrmondragon to pick this up, timeboxed to a 4 within the timeline for Tap-Toberfest.

Does that sound okay?

[tayloramurphy]

@aaronsteers yep - sounds good cc @edgarrmondragon