Bug 21625: Fix wording and typo in SMSSendDriver system preference description

Bug 21625: Fix wording and typo in SMSSendDriver system preference description

SMSSendDriver was missing an S.
Koha is sending not receiving messages, so I think switching
that will be a little more clear.

To test:
Verify that the system preference description reads correctly.

Signed-off-by: Andreas Roussos <arouss1980@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 9d0fc26c4335fc9be7a01e3069c458e9397fc94f)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>