sys_util: terminal: remove the Pollable trait impl as it is not used
sys_util: terminal: remove the Pollable trait impl as it is not used

Signed-off-by: Constantin Musca <e6b0bba089ab6d3e8fde8b62faae63e6b21d7743@amazon.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker