Remove parity namespace and refs

[wolovim]

What was wrong?

• Parity has long been sunset. The namespace within web3.py doesn't need maintaining.
• Node-related docs have gotten nice and stale in a few locations. Removed some stated preferences and replaced links with ethereum.org so they can maintain lists of tools over time.

(Note: we didn't rush into ripping this functionality out given feedback at various points that some users still used tracing features via OpenEthereum or modded Parity nodes. If you are negatively impacted by this code removal, you can use custom methods or external modules to introduce non-standard features.)

v6 breaking change related to: #1416

Todo:

• Add entry to the release notes

Cute Animal Picture

[pacrob]

lgtm!

[kclowes]

🎉 !