[TASK] Remove adding module_sys_dmail_category in ext_tables.php

This is already present in ext:direct_mail. Since it is only
added when direct_mail is installed it is not needed.

Further is the translation for label missing so it adds an
incomplete TCA configuration.

Change-Id: I78aa23ba1b35fa2665f375ca800ccccaaaa4d5cd
Reviewed-on: https://review.typo3.org/30348
Reviewed-by: Sebastian Fischer
Tested-by: Sebastian Fischer