trace_replay: replace unicode "µ" with "u" in log output

Unicode log output isn't supported by CrOS autotest. Periodically,
graphics_TraceReplayExtended.* autotest tests fail with a
UnicodeDecodeError exception after encountering the unicode "µ"
character. This CL simply replaces with "u".

BUG=b:182290297
TEST=tast run -buildbundle=cros \
     -var=keepState=true        \
     $DUT graphics.TraceReplayExtended.glxgears_1minute

Change-Id: I2eb3f8494565e82b727d451d4de114905dd6428d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/graphics/+/2876252
Tested-by: Ryan Neph <ryanneph@google.com>
Auto-Submit: Ryan Neph <ryanneph@google.com>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
Reviewed-by: Po-Hsien Wang <pwang@chromium.org>
Commit-Queue: Po-Hsien Wang <pwang@chromium.org>