SF: Use RAII for TransactionTracing

Ensure the thread joins on destruction, which had been suppressed by a
leak fixed by ag/16613874.

Bug: 214486764
Test: libsurfaceflinger_arc_test
Test: libsurfaceflinger_unittest
Change-Id: Ib766735dc51e89d63080dd6b9afe8464da7c1c6a