Revert "client: add filename and line in logging"

This reverts commit 0007b8debcbd1d1db390b88c764acfa56a3b2696.

Reason for revert: crbug.com/1070407

Original change's description:
> client: add filename and line in logging
> 
> This is to help to know where the log come from.
> 
> Bug: 1061531
> Change-Id: I1c172fce98aa4ab746a2b3c0a0de6e39c7faa0fb
> Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2127186
> Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
> Commit-Queue: Junji Watanabe <jwata@google.com>
> Reviewed-by: Junji Watanabe <jwata@google.com>


# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1061531, 1070407
Change-Id: I0c2664c9344bc908f81e795baf9e7aa4cea935e1
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2147576
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Junji Watanabe <jwata@google.com>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Mirrored-From: https://chromium.googlesource.com/infra/luci/luci-py
Cr-Mirrored-Commit: 88c13ad6d291dcd189fd92bccc5f0df24ab4ea06
diff --git a/utils/logging_utils.py b/utils/logging_utils.py
index 2d185e1..14e3c3d 100644
--- a/utils/logging_utils.py
+++ b/utils/logging_utils.py
@@ -183,9 +183,7 @@
   Makes it log in UTC all the time. Prepare a rotating file based log.
   """
   assert not find_stderr(root)
-  formatter = UTCFormatter(
-      '%(process)d %(asctime)s %(severity)s %(pathname)s %(lineno)d:'
-      ' %(message)s')
+  formatter = UTCFormatter('%(process)d %(asctime)s %(severity)s: %(message)s')
 
   # It is a requirement that the root logger is set to DEBUG, so the messages
   # are not lost. It defaults to WARNING otherwise.