Fixing chrome_proxy_wpr_record.py warning
Fixing chrome_proxy_wpr_record.py warning

https://github.com/python/cpython/commit/a2670565d8f5c502388378aba1fe73023fd8c8d4
^ requires text mode is forced in order to buffer py3 lines.
This CL causes conversion to/from text in the subprocess module
so the encode/decode can be removed.

Bug: chromium:1243101
Change-Id: Ie712ba78e18a8e645053f7b1041d1adca8024d09
Reviewed-on: https://chromium-review.googlesource.com/c/catapult/+/3116820
Commit-Queue: Ari Chivukula <1040b02f8ada0933be490bb2afe80a07f3cef9d5@chromium.org>
Auto-Submit: Ari Chivukula <1040b02f8ada0933be490bb2afe80a07f3cef9d5@chromium.org>
Reviewed-by: Andrew Bennetts <f07c55753dac44d78e0294a1d64ea321baaa78f4@google.com>
Reviewed-by: Dan H <2e8715460253355fb9e8bf01cf6fb682a6fd4c62@chromium.org>

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