mail/postsrsd: Update to 1.4, avoid secret in pkg

Update to 1.4 (1)
While here, avoid creating postsrsd.secret in package and improve rc script (2)

PR: 211098 (2)
PR: 217340 (1)
Submitted by: Miroslav Lachman (2)
Submitted by: Peter Putzer (1)
Approved by: Krzysztof <ports@bsdserwis.com> (maintainer) (1)(2)