That’s right, the offboard compressor is dead. No longer are offboard compressor systems legal for FRC.
Section 10.9 - Pneumatic System no longer contains a rule detailing the use of an offboard compressor (Section 8.9, R91 in the Power Up manual), nor does it contain a rule permitting offboard compressors (Section 8.9, R86 in the Power Up manual).
Furthermore, all references to an offboard system have been removed: See below the blue box for R86 compared to the blue box for the same rule (R85) in Power Up.
Note also that the robot weight limit has increased to 125lb from 120lb in 2018, and that the weight of an FRC compressor is approximately 3lb with its associated fittings and supporting components. The weight allowance seems to have been borrowed from bumpers.