Andy Postnikov opened merge request !106808: community/synapse: drop unused py3-txacme dependency at alpine / aports

Synapse removed its ACME support years ago: txacme appears nowhere in the package metadata, not even as an optional extra, and no synapse module imports it. py3-txacme is also broken on edge -- txacme 0.9.3 (2020) fails to import under python 3.