kunit: tool: unmark test_data as binary blobs

The tools/testing/kunit/test_data/ directory was marked as binary
because some of the test_data files cause checkpatch warnings. Fix this
by dropping the .gitattributes file.

Fixes: afc63da6 ("kunit: kunit_parser: make parser more robust")
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>