Why does the Huey have this weird hump as shown in the picture? For some system? Why not remove it?
It's a bit of structure to guide the rotor forces into the rest of the airframe, it would not be good if this bit went missing.
Fwd/aft, left/right, up/down. The rotor provides the lifting forces and driving forces and these are quite concentrated around the rotor axis. Picture the airframe like an empty beer can - some panels are required to cope with the forces while remaining in shape.
It's where the main rotor transmission and control servos are housed. The forward bulkhead of the "hump" WAS the entire aft cabin bulkhead of the original Huey models. Starting with the D model (I Think) the cabin was extended around the transmission tunnel to form what are called the right and left alcoves. The original shorter body Hueys were adapted to the gunship roles.
Click to view, cropped from https://forums.eagle.ru/showthread.php?t=98895
The biggest feature in that area is the fuel tank, which is roughly 0.65 m$^3$ (165 US gal). With a cabin height of 1.2 m (it's not a standing cabin), the base (assuming square) would be 0.74 x 0.74 m (2'5" x 2'5") of floor area, which does look right.