kunit: tool: minor cosmetic cleanups in kunit_parser.py

There should be no behavioral changes from this patch.

This patch removes redundant comment text, inlines a function used in
only one place, and other such minor tweaks.

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>