Remove deadcode from depot_tools scripts

Removing some deadcode from depot_tools scripts. More follow-up CLs will
be made after this to remove more dead code.

R=sokcevic,gavinmak

Change-Id: Iad20e9e1737e49c1370248d32c6317cf2be63de4
Bug: 1475776
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4811216
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

metrics.py

@@ -10,7 +10,6 @@ import functools
 import json
 import os
 import sys
-import tempfile
 import threading
 import time
 import traceback