refactor: drop proxy-supports-routes capability trigger

The trigger was added to refuse proxy:route:set under openresty and haproxy, but the hard refusal created an ordering dependency for declarative tools and blocked users from staging routes ahead of a backend switch. Routes are now stored regardless of the active backend and silently ignored by backends that do not render them; the docs call out the inert behavior under openresty and haproxy.

plugins/nginx-vhosts/proxy-supports-routes

@@ -1,18 +0,0 @@
-#!/usr/bin/env bash
-set -eo pipefail
-[[ $DOKKU_TRACE ]] && set -x
-source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
-
-trigger-nginx-vhosts-proxy-supports-routes() {
-  declare desc="advertises path-based routing support for nginx"
-  declare trigger="proxy-supports-routes"
-  declare APP="$1"
-
-  if [[ "$(plugn trigger proxy-type "$APP")" != "nginx" ]]; then
-    return
-  fi
-
-  echo "true"
-}
-
-trigger-nginx-vhosts-proxy-supports-routes "$@"