Remove unused EME v0.1b MediaKeyError values.

tools/metrics/histograms/histograms.xml

 <!--
 Copyright 2013 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 16015 matching lines @@
   <int value="33" label="SWF (ShockWave Flash)"/>
   <int value="34" label="VC-1"/>
   <int value="35" label="WAV / WAVE (Waveform Audio)"/>
   <int value="36" label="Matroska / WebM"/>
   <int value="37" label="WTV (Windows Television)"/>
 </enum>
 
 <enum name="MediaKeyError" type="int">
   <int value="1" label="kUnknownError"/>
   <int value="2" label="kClientError"/>
-  <int value="3" label="kServiceError"/>
-  <int value="4" label="kOutputError"/>
-  <int value="5" label="kHardwareChangeError"/>
-  <int value="6" label="kDomainError"/>
 </enum>
 
 <enum name="MediaKeyException" type="int">
   <int value="0" label="kUnknownResultId"/>
   <int value="1" label="kSuccess"/>
   <int value="2" label="kKeySystemNotSupported"/>
   <int value="3" label="kInvalidPlayerState"/>
 </enum>
 
 <enum name="MouseEventFollowedByClick" type="int">
@@ skipping 3586 matching lines @@
   <group name="Disabled" label="Neither extra webstore link is visible"/>
   <group name="FooterLink" label="Link in bottom right of footer"/>
   <group name="PlusIcon" label="Plus icon in apps page"/>
   <affected-histogram name="Extensions.AppLaunch"/>
   <affected-histogram name="NewTabPage.DefaultPageType"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>