Windscribe incompatibility (solved)

This isn't a question, but a problem solved, posted in case anyone else runs into a similar issue. If I had a question, it would be "where the heck did the handy Network Diagnostics app that used to be in Core Services go in High Sierra?"

tl;dr -- if you use Windscribe, update to v1.70 prior to installing 10.13. If you used to use Windscribe, and lose all network connectivity after your High Sierra installation, delete the com.aaa.windscribe.* files in /Library/LaunchDaemons.

Problem: After installation of High Sierra on a 2012 MacBook Air, there was no wired or wireless connectivity past the WAN router (and no DNS resolution, etc), though everything looked fine in the setup, DHCP worked, and there had been no changes other than High Sierra installation. Everything worked normally in Safe Mode, and from Recovery, so problem was likely a startup item.

Long story short, the issue was Windscribe v1.61 Build 9 -- I had tested WindScribe (VPN provider) at one point, but it wasn't active. The leftover /Library/LaunchDaemons/com.aaa.windscribe.firewall_on.plist file was the specific culprit (the Windscribe firewall is intended to disable internet connectivity when not connected to their network, but wasn't in use on that laptop prior to High Sierra installation -- not sure why the plist file had been left behind).

The upside was a good excuse to go clean out obsolete and unnecessary files in /Library/LaunchAgents, /Library/LaunchDaemons, etc.