Bug 4461: Simplify recipients code

Bug 4461: Simplify recipients code

As the feature is now turned off without KohaAdminEmailAddress, we only
need to check if the email address of the library if defined.
Not that we should not check for $library->branchreplyto or
ReplytoDefault, but only $library->branchemail, as we do everywhere else
(I think)

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>