chore: update Mercure configuration in Caddyfile (#766)

Due to dunglas/mercure#939 and the deprecation message, it makes sense to apply the edits to update the Mercure configuration.

See https://github.com/dunglas/mercure/blob/main/docs/UPGRADE.md#017

Author: 7-zete-7

frankenphp/Caddyfile

@@ -23,8 +23,6 @@
 	encode zstd br gzip
 
 	mercure {
-		# Transport to use (default to Bolt)
-		transport_url {$MERCURE_TRANSPORT_URL:bolt:///data/mercure.db}
 		# Publisher JWT key
 		publisher_jwt {env.MERCURE_PUBLISHER_JWT_KEY} {env.MERCURE_PUBLISHER_JWT_ALG}
 		# Subscriber JWT key