Cleanup from v2 to v3 removing ssfn files

[davidmfinol]

Changes

• Cleanup from v2 to v3 removing ssfn files

Checklist

• Read the contribution guide and accept the code of conduct
• Readme (updated or not needed)
• Tests (added, updated or not needed)

[davidmfinol]

I believe the test run failed because we need to do step 5 of https://github.com/game-ci/steam-deploy#configvdf
However, I don't remember who provided the Steam builder account that we are using.

[davidmfinol]

I've provided new credentials for the STEAM_USERNAME and STEAM_CONFIG_VDF secrets.
Accordingly also updated the TEST_APP_ID and removed the first depot override.