[cleanup] Clean up trace event tests by removing macros

The macros take implicit local arguments and make the tests harder to
read. Remove the macros and add a helper to get size directly given
this is the only use of the helper that returns the whole list.

Remove the typedef of vector of trace events, because it is only used
in two places now and is also called 'list' not vector.

Use unique pointers for the ownership of MockTraceObject.

Change-Id: Iec495c436cf7326224137321a84035c817622eaa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1538131Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60443}