Sentinel probe was indeed deleted due to weight issues. Operation 'Weight Watchers' was a major last-ditch part of the program to get Sentinel down to a flyable weight. Safety systems were deleted, military kit deleted, kit redesigned to save the odd kg here and there, wiring gauge limits pushed, crew facilities reduced, equipment rack strength reduced, crash and ditch structure abandoned, safe separation limits ignored and even the whole internal cabin liner was binned - the aircraft still flies with 'single use transit trim' with multiple efforts trying to keep it attached to the interior and not falling across the crew or (god forbid) exit doors.