Removed the gpgme_set_signature_algorithm stuff. We can't add a

Removed the gpgme_set_signature_algorithm stuff.  We can't add a
function to our API without discussion the consequences of.  By design
the signature algorithm is a property of the signer's key and can't be
set arbitrary.  The library is named GnuPG Made Easy so we should not
burden the user with an API to select stuff which can only be done by
the backend.  Changes in gpgme require support by the backend.  If we
have the requirement to implement it, it will be done as a global
configuration option for signers or as meta-data asscociated with a
certificates for recipients. I habe not found this as a requirement of
the Aegypten project.