Remove unused imports in depot_tools/*.py

I know that sometimes imports can have side-effects,
so unused imports shouldn't always be removed, but these
ones look like they could be.

Change-Id: Iea9f82afa99b0ea35f29a28f20ce0493b579cfee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1819860
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>

buildbucket.py

@@ -22,7 +22,6 @@ import json
 import urlparse
 import os
 import sys
-import time
 
 from third_party import httplib2
 

gclient_scm.py

@@ -24,7 +24,6 @@ try:
 except ImportError:  # For Py3 compatibility
   import urllib.parse as urlparse
 
-import download_from_google_storage
 import gclient_utils
 import git_cache
 import scm

git_cache.py

@@ -24,8 +24,6 @@ try:
 except ImportError:  # For Py3 compatibility
   import urllib.parse as urlparse
 
-import zipfile
-
 from download_from_google_storage import Gsutil
 import gclient_utils
 import subcommand

my_activity.py

@@ -38,7 +38,6 @@ import collections
 import contextlib
 from datetime import datetime
 from datetime import timedelta
-from functools import partial
 import itertools
 import json
 import logging

ninjalog_uploader.py

@@ -23,7 +23,6 @@ import logging
 import multiprocessing
 import os
 import platform
-import socket
 import subprocess
 import sys
 import time

roll_dep.py

@@ -12,8 +12,6 @@ script will always roll to the tip of to origin/master.
 from __future__ import print_function
 
 import argparse
-import collections
-import gclient_eval
 import os
 import re
 import subprocess

scm.py

@@ -6,14 +6,10 @@
 
 import glob
 import io
-import logging
 import os
 import platform
 import re
 import sys
-import tempfile
-import time
-from xml.etree import ElementTree
 
 import gclient_utils
 import subprocess2