GCP related build workflow updates

[andy-neuma]

SUMMARY:

• overall this removes dependencies for being on the VPC/VPN from the build stage, e.g. installing "magic wand nightly" from private pypi
• removes redundant python lint check step, deprecates lint action, and removes lint info from summary
• makes python VENV creation more robust when the VENV already exists

TEST PLAN:
runs on remote push using our AWS runners. this has been green. i've also manually ran the build workflow on GCP static runners.