kunit: drop unused assert_type from kunit_assert and clean up macros

This field has been split out from kunit_assert to make the struct less
heavy along with the filename and line number.

This change drops the assert_type field and cleans up all the macros
that were plumbing assert_type into kunit_assert.

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>