matrixsynapse: Handle migration to 1.0

Matrix Synapse has two ports - 8008 for communication with clients and 8448 for federation with other servers. Both need some kind of TLS certificates. Our LE certs on Apache take care of client communication (8008). We leave the port 8448 open in the firewall for federation.

Matrix versions before 0.99 have used self-signed certificates. 0.99 will transparently talk to LE client and get a LE cert of the Matrix server for federation as well. Version 1.0 onwards, all server to server communication will require each server to have a CA-issued certificate.

The recommended action for now is to delete the self-signed certificates while upgrading to 0.99. This is probably best handled in the Debian package itself.

Reference: See this FOSDEM video at around 35 minutes