tests: remove non-existent files from EXTRA_DIST

tests: remove non-existent files from EXTRA_DIST

These files were removed in commit

    e8bacbe2bd42 ("Remove stale trace-ir test files")

... so they should be removed from EXTRA_DIST as well.  Currently, it
causes a "make dist" failure:

  make[4]: *** No rule to make target 'test_trace.py', needed by 'distdir'.  Stop.

The tests/lib/trace-ir directory is currently not very useful, as it
contains no tests at all, so we could remove it in theory.  But I
presume we'll add something in there in not too long, so I think we can
leave it there.

Change-Id: Iec44efd7c52e84b35a5a55206055b5d63635fbe1
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1241
Tested-by: jenkins
Reviewed-by: Jonathan Rajotte Julien <jonathan.rajotte-julien@efficios.com>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>