Don't use newsfiles for config changes

per discussion today

changelog.d/13169.config

@@ -1 +0,0 @@
-[`rc_joins_per_room`](https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#rc_joins_per_room): parameters for the per-room join rate limit.

pyproject.toml

@@ -9,11 +9,6 @@
         name = "Features"
         showcontent = true
 
-    [[tool.towncrier.type]]
-        directory = "config"
-        name = "Config options"
-        showcontent = true
-
     [[tool.towncrier.type]]
         directory = "bugfix"
         name = "Bugfixes"