Remove hardcoded rate limit value

Name is chosen to match the equivalent setting in the configuration
of the rate limits for edits.

Fixes #4427.

config/settings/test.yml

@@ -21,6 +21,7 @@ trace_image_storage: "test"
 trace_icon_storage: "test"
 # Lower some rate limits for testing
 max_changeset_comments_per_hour: 10
+comments_to_max_changeset_comments: 20
 moderator_changeset_comments_per_hour: 15
 # Private key for signing id_tokens
 doorkeeper_signing_key: |