helm-chart: remove deprecated use of traefik middleware's forceSlash option (#853)

forceSlash is deprecated by traefik

Author: gardleopard

resources/helm/dask-gateway/templates/gateway/middleware.yaml

@@ -20,5 +20,4 @@ spec:
   stripPrefix:
     prefixes:
       - '{{ .Values.gateway.prefix | trimSuffix "/" }}'
-    forceSlash: false
 {{- end }}