Remove 'utc' field from TimeSlicedOutput conf to prevent ConfigError

Helpers/Compat utils can't judge user specifies both localtime/utc or converted result.
This changes conf dumpped result but it seems acceptable.

lib/fluent/compat/output.rb

@@ -621,6 +621,7 @@ def configure(conf)
           elsif conf['utc']
             conf['timezone'] = "+0000"
             conf['localtime'] = "false"
+            conf.delete('utc')
           elsif conf['localtime']
             conf['timezone'] = Time.now.strftime('%z')
             conf['localtime'] = "true"

test/test_output.rb

@@ -203,6 +203,16 @@ def create_driver(conf=CONFIG)
       Fluent::Test::TimeSlicedOutputTestDriver.new(TimeSlicedOutputTestPlugin).configure(conf, true)
     end
 
+    data(:none => '',
+         :utc => "utc",
+         :localtime => 'localtime',
+         :timezone => 'timezone +0000')
+    test 'configure with timezone related parameters' do |param|
+      assert_nothing_raised {
+        create_driver(CONFIG + param)
+      }
+    end
+
     sub_test_case "test emit" do
       setup do
         @time = Time.parse("2011-01-02 13:14:15 UTC")