Remove dashboard Python test runner copy dashboard/bin/run_tests.
Remove dashboard Python test runner copy dashboard/bin/run_tests.

Currently dashboard/bin/run_tests is a copy of run_py_tests
which was necessary until https://codereview.chromium.org/1353963003/.

A different dashboard/bin/run_tests which runs both JS and Python tests
may be added later.

Review URL: https://codereview.chromium.org/1376543002

benschmaus/catapult,SummerLW/Perf-Insight-Report,sahiljain/catapult,benschmaus/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult,benschmaus/catapult,0x90sled/catapult,benschmaus/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult-csm,sahiljain/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult,sahiljain/catapult,benschmaus/catapult,catapult-project/catapult,SummerLW/Perf-Insight-Report,sahiljain/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult,0x90sled/catapult,catapult-project/catapult,sahiljain/catapult,catapult-project/catapult-csm,SummerLW/Perf-Insight-Report,sahiljain/catapult,benschmaus/catapult,0x90sled/catapult,catapult-project/catapult