[TASK] Code cleanup in CLI script

The commandline descriptions in "cli/cli_direct_mail.php" are just
dummies. Change them to reflect the expected values: Set description
and available options and call example.

Additionally also change the name of the instanciated object
"$cleanerObj" to "$mailerObj" as this is obviously a relict.

Change-Id: I71c495aba6c5aa51b343a168926392c7c18b394f
Resolves: #54462
Releases: 4.0
Reviewed-on: https://review.typo3.org/26456
Reviewed-by: Bernhard Kraft
Tested-by: Bernhard Kraft