What this mosfet really needed on the STUSB4500?
MOSFET T4 is to ensure the cold socket, preventing incoming negative voltage on VBUS.
Removing T4 can save the cost and PCB space, but it will not be protected for negative voltage nor reverse battery - the reverse current flowing from the battery charger to the Source.
To remove it or to keep it depends on the application needs for the protection.
MOSFET T1 acts as a ON-OFF switch, to guarantee no load when the device is not attached to a Source.
Consider it as something must. Removing T1 may have a drawback not compliant to the standard.