Remove EncodingAPI runtime flag(status=stable)

Source/modules/encoding/TextDecoder.idl

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 11 matching lines @@
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 [
-    RuntimeEnabled=EncodingAPI,
     Exposed=(Window,Worker),
     Constructor(optional DOMString label = "utf-8", optional TextDecoderOptions options),
     RaisesException=Constructor,
     GarbageCollected,
     MeasureAs=TextDecoderConstructor
 ] interface TextDecoder {
     readonly attribute DOMString encoding;
     readonly attribute boolean fatal;
     readonly attribute boolean ignoreBOM;
     [RaisesException, MeasureAs=TextDecoderDecode] DOMString decode(optional ArrayBufferView input, optional TextDecodeOptions options);
 };