Use only one parameter for StopTracing

We can stop tracing either when aborting where we don't want to flush
the entries and stop immediately or when stopping tracing where we want
to flush any data and then stop tracing. We used to use two parameters
finish_tracing and flush_file but we just need one.

Bug: 259258187
Test: art/test.py
Change-Id: I6d25a56790d82a55ecd679b7157bd1995fc5258d
2 files changed