[NFC] Remove @devhigley/parse-proxy as a dependency

[pnappa]

This is a random package written by someone, which serves as a risk for supply chain integrity. There is no trusted publishing established for this package, so there's a high risk that it could be taken over & cause an attack against all your consumers.

The package isn't very well written, and has some bad handling for cases which are likely to be brought up. The behaviour can be fully implemented using builtins.

For example, localhost:8000 throws, which is a fairly common path to handling proxies, whilst IPv6 support is also non-existent (e.g. http://[::1]:8080 throws).

[pnappa]

As an aside, literally the only public dependencies of this package are other docusign packages, so I assume it's prudent to go and remove them from the other packages too? Ideally the signature for the docusign client would accept proxy options similar to what axios accepts, but this would be a breaking change, so I decided on keeping the string based proxy definition.

[pnappa]

Another important note is that there's a few other dependencies which could be taken out:

• csv-stringify is not even used at all, it only exists in commented out code (in test/, which means it should be a devDependency WHEN it's used).
• safe-buffer is not needed, as it's only ever referenced in var Buffer = global.Buffer.from ? global.Buffer : require('safe-buffer').Buffer;, which is impossible, as this library requires Node v12+ (Buffer.from was added in ~v8)
• I believe passport-oauth2 is unused in practice, I haven't done a deep enough audit for it, but it seems sus