The nix-bundled rbw (1.13.2) had a protocol mismatch with newer system
rbw-agent versions. The agent sends environment variables as byte arrays,
but rbw 1.13.2 expects base64-encoded strings, causing:
rbw unlocked: failed to parse message '...': invalid type: sequence,
expected base64 encoded os string
By not bundling rbw in the nix package, the script uses the system rbw
which matches the running rbw-agent and can communicate correctly.
Fixes gcr-tth
