modules/sasl: disable DH-BLOWFISH & AES by default

Atheme has dropped them in their git version.
https://github.com/atheme/atheme/commit/15f6d84

I would also like EXTERNAL to be trid by default, but \*Cert and \*CertFP
aren't so used and that wouldn't probably be accepted.
Merge pull request #673 from Mkaysi/sasl

modules/sasl: disable DH-BLOWFISH & AES by default