FIx missing import of urllib.error. Also remove unneeded time import.

Change-Id: I708e13ea6fd56ceec2cd6faa0928448b6a6a6964
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/7260375
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Philipp Wollermann <philwo@google.com>
Commit-Queue: Alex Ovsienko <ovsienko@google.com>
Reviewed-by: Nico Weber <thakis@google.com>

ninjalog_uploader.py

@@ -31,7 +31,7 @@ import platform
 import re
 import subprocess
 import sys
-import time
+import urllib.error
 import urllib.request
 
 import build_telemetry