[Signin]: Fix crash in |signin_email_confirmation_ui|.

We get a crash in the |signin_email_confirmation_ui| due to a |DCHECK|
|HasUnexpectedPlaceholder()|that checks that the replacement does not
have an unsubstituted placeholder.  The |DCHECK| runs before some of the
placeholders get replaced by JavaScript.  To avoid this crash, we
remove the placeholders from |signin_email_confirmation.html| and rely
on JavaScript to replace correctly the text.

Change-Id: Ib56b8fbc4ae0d042ecffb53912a111a4964afb11
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1878769Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Commit-Queue: Monica Basta <msalama@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719549}

chrome/browser/resources/signin/signin_email_confirmation/signin_email_confirmation_app.html

@@ -46,7 +46,6 @@
     </style>
     <div class="container">
       <div class="top-title-bar" id='dialogTitle'>
-          $i18n{signinEmailConfirmationTitle}
       </div>
       <div class="details">
         <cr-radio-group selected="createNewUser">
@@ -57,7 +56,6 @@
             </div>
             <div class="radio-button-subtitle-container"
                 id="createNewUserRadioButtonSubtitle">
-              $i18n{signinEmailConfirmationCreateProfileButtonSubtitle}
             </div>
           </cr-radio-button>
           <cr-radio-button id="startSyncRadioButton" name="startSync">
@@ -66,7 +64,6 @@
             </div>
             <div class="radio-button-subtitle-container"
                 id="startSyncRadioButtonSubtitle">
-              $i18n{signinEmailConfirmationStartSyncButtonSubtitle}
             </div>
           </cr-radio-button>
         </cr-radio-group>