Remove unused content .rc files.

content/app/strings/content_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- This file contains definitions of resources that will be translated for
 each locale. Specifically, these are UI strings that are used by content that
 need to be translated for each locale.-->
 
 <!-- Some of these strings and string descriptions were taken from
 WebKit/win/WebCoreLocalizedStrings.cpp so we include the original license
 below:
 
@@ skipping 27 matching lines @@
       source_lang_id="en" enc_check="möl">
   <outputs>
     <!-- TODO add each of your output files.  Modify the three below, and add
     your own for your various languages.  See the user's guide
     (http://wiki/Main/GritUsersGuide) for more details.
     Note that all output references are relative to the output directory
     which is specified at build time. -->
     <output filename="grit/content_strings.h" type="rc_header">
       <emit emit_type='prepend'></emit>
     </output>
-    <!-- TODO(tony): Get rid of this .rc file. -->
-    <output filename="content_strings_en-US.rc" type="rc_all" lang="en" />
-
     <output filename="content_strings_am.pak" type="data_package" lang="am" />
     <output filename="content_strings_ar.pak" type="data_package" lang="ar" />
     <if expr="use_third_party_translations">
       <output filename="webkit_strings_ast.pak" type="data_package" lang="ast" />
     </if>
     <output filename="content_strings_bg.pak" type="data_package" lang="bg" />
     <output filename="content_strings_bn.pak" type="data_package" lang="bn" />
     <if expr="use_third_party_translations">
       <output filename="webkit_strings_bs.pak" type="data_package" lang="bs" />
     </if>
@@ skipping 694 matching lines @@
         Please lengthen this text to <ph name="MIN_CHARACTERS">$2<ex>101</ex></ph> characters or more (you are currently using <ph name="CURRENT_LENGTH">$1<ex>100</ex></ph> characters).
       </message>
 
       <message name="IDS_PLUGIN_INITIALIZATION_ERROR" desc="A message displayed when a plugin failed to load">
         Couldn't load plugin.
       </message>
 
     </messages>
   </release>
 </grit>