out_file: Avoid performing multi-worker check in configure()

The check did not work well with `<worker 0-N>` directive for
the following reasons:

 * When Fluentd starts up, supervisor performs sanity check on
   configuration by creating actual instances of plugins.

 * This check precedes SeverModule, which prepares various assets
   for workers (lockdir, RPC endpoints and shared sockets etc.)

 * Fluent::Plugin::Base dynamically overrides `system_config.workers`
   during start-up, and leaves the value > 1 only when `<worker 0-N>`
   directive is used.

Fix this issue by avoiding faulty sanity check in `configure()`.

Signed-off-by: Fujimoto Seiji <[email protected]>

lib/fluent/plugin/out_file.rb

@@ -188,10 +188,6 @@ def configure(conf)
         condition = Gem::Dependency.new('', [">= 2.7.0", "< 3.1.0"])
         @need_ruby_on_macos_workaround = true if condition.match?('', RUBY_VERSION)
       end
-
-      if @need_lock && @append && @fluentd_lock_dir.nil?
-        raise Fluent::InvalidLockDirectory, "must set FLUENTD_LOCK_DIR on multi-worker append mode"
-      end
     end
 
     def multi_workers_ready?