Reverts flutter/flutter#140521
Initiated by: zanderso
This change reverts the following previous change:
Original Description:
Original PR: https://github.com/flutter/flutter/pull/138057
Revert: https://github.com/flutter/flutter/pull/140502
Issue: https://ci.chromium.org/ui/p/flutter/builders/prod/Linux_android%20flutter_test_performance/12787/overview
Exception: flutter test rendered unexpected output (1 bad lines)
Explanation: leak tracker adds tear down even when there is no leak tracking, because at the moment of adding tear down it is unclear if leak tracking will be used for some tests.
Fix: add enabling flag for leak tracker and make creation of tear down conditional.
Prerequisites: