[TASK] Adapt unit-tests to new mail-adapter-hook

 (for t3lib_utility_mail)

Adjust the unit-tests to the updated interface
instead of the deprecated one. The deprecated
interface was removed with 4.7
(commit 97a6f07f).

Change-Id: I76f6bb24a58ab7f4d487e596e2abedb1da9767da
Resolves: #33850
Releases: 4.7
Reviewed-on: http://review.typo3.org/8973
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Steffen Gebert
Tested-by: Steffen Gebert