Use line buffering for the input and output ports

As these are used for logging, which is done on a line by line basis. Remove
the now redundant calls to (force-output).

scripts/guix-data-service-process-jobs.in

@@ -27,6 +27,9 @@
              (guix-data-service database)
              (guix-data-service jobs))
 
+(setvbuf (current-output-port) 'line)
+(setvbuf (current-error-port) 'line)
+
 (with-postgresql-connection
  (lambda (conn)
    (simple-format #t "Ready to process jobs...\n")

scripts/guix-data-service.in

@@ -80,6 +80,9 @@
      (error "extraneous argument" arg))
    %default-options))
 
+(setvbuf (current-output-port) 'line)
+(setvbuf (current-error-port) 'line)
+
 (let ((opts (parse-options (cdr (program-arguments)))))
   (let ((repl-port (assoc-ref opts 'listen-repl)))
     (when repl-port