ata: remove stale maintainership information from core code

In commit 7634ccd2

 ("libata: maintainership update") from 2018
Jens has officially taken over libata maintainership from Tejun so
remove stale information from core libata code.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>