Disable PID in logs for Builtin engine

[bryantcj52]

References:
#1915
#2176

It seems this feature was added for apache and niginx but it does not work for the builtin engine:
passenger start --disable-log-prefix Could not start the server engine: ERROR: unrecognized argument --disable-log-prefix. Please type '/usr/lib64/passenger/support-binaries/PassengerAgent watchdog --help' for usage.

It doesn't work in the Passengerfile.json either.

passenger --version
Phusion Passenger 6.0.6

[BretFisher]

The documentation says this works for PASSENGER_ENGINE=builtin but it doesn't. Had to switch to nginx to get it working.