[cli] remove unused imports (#1001)

colossalai/cli/benchmark/__init__.py

-from random import choices
 import click
 
 from .utils import *

colossalai/cli/benchmark/utils.py

 import math
 import time
-from grpc import Call
 import torch
 
 from colossalai.utils import MultiTimer
-from colossalai.core import global_context as gpc
 from colossalai.context import ParallelMode, Config
 from typing import List, Dict, Tuple, Callable
 

colossalai/cli/launcher/multinode_runner.py

 import fabric
-from fabric import Connection
 from .hostinfo import HostInfo, HostInfoList
 from multiprocessing import Pipe, Process
 from multiprocessing import connection as mp_connection