[direnv] Redirect use flake to /dev/null if COMM_NIX_LOGGING_LEVEL is "none"
Summary: Found the logging to be kind of annoying. Would prefer if Nix/Direnv worked completely in the background. Realize this is a personal preference so this change won't affect anyone unless they explicitly set COMM_NIX_LOGGING_LEVEL="none".
Before setting COMM_NIX_LOGGING_LEVEL:
After setting COMM_NIX_LOGGING_LEVEL="none":
Reviewers: jon, ginsu, bartek, varun
Reviewed By: varun
Differential Revision: https://phab.comm.dev/D7052