Remove webstore code for signin that is no longer used.

chrome/common/extensions/api/webstore_private.json

 // Copyright (c) 2012 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.
 
 [
   {
     "namespace":"webstorePrivate",
     "description": "none",
     "functions": [
       {
@@ skipping 111 matching lines @@
           },
           {
             "name": "callback",
             "type": "function",
             "description": "Called when the user has either accepted/rejected the dialog, or some error occurred (such as invalid manifest or icon image data).",
             "optional": true,
             "parameters": [
               {
                 "name": "result",
                 "type": "string",
-                "description": "A string result code, which will be empty upon success. The possible values in the case of errors include 'unknown_error', 'user_cancelled', 'manifest_error', 'icon_error', 'invalid_id', 'permission_denied', 'invalid_icon_url', 'signin_failed', and 'already_installed'."
+                "description": "A string result code, which will be empty upon success. The possible values in the case of errors include 'unknown_error', 'user_cancelled', 'manifest_error', 'icon_error', 'invalid_id', 'permission_denied', 'invalid_icon_url' and 'already_installed'."
               }
             ]
           }
         ]
 
       },
       {
         "name": "completeInstall",
         "description": "",
         "parameters": [
@@ skipping 109 matching lines @@
             "name": "callback",
             "type": "function",
             "optional": false,
             "parameters": [
               { "name": "is_incognito", "type": "boolean" }
             ]
           }
         ]
       },
       {
-        "name": "signIn",
-        "description": "Signs the user into Chrome.",
-        "parameters": [
-          {
-            "name": "continue_url",
-            "type": "string",
-            "description": "The continue URL to navigate to once sign-in completes."
-          },
-          {
-            "name": "callback",
-            "type": "function",
-            "description": "Called if the user is already signed in or if the sign-in method was invoked incorrectly (e.g. with an invalid continue URL), sign-in is unavailable (e.g. in Incognito), or the API was not called in response to a user gesture. Upon such a failure, chrome.runtime.lastError will be set to 'invalid_continue_url', 'signin_is_disallowed', 'signin_failed', 'merge_session_failed', or 'user_gesture_required'.",
-            "optional": true,
-            "parameters": []
-          }
-        ]
-      },
-      {
         "name": "getEphemeralAppsEnabled",
         "description": "Returns whether the ephemeral apps feature is enabled.",
         "parameters": [
           {
             "name": "callback",
             "type": "function",
             "optional": false,
             "parameters": [
               { "name": "is_enabled", "type": "boolean" }
             ]
@@ skipping 20 matching lines @@
                 "enum": ["success", "user_gesture_required", "unknown_error", "feature_disabled", "unsupported_extension_type", "missing_dependencies", "install_error", "user_cancelled", "invalid_id", "blacklisted", "blocked_by_policy", "install_in_progress", "launch_in_progress"],
                 "description": "Whether an attempt to launch an app succeeded, or the reason for failure."
               }
             ]
           }
         ]
       }
     ]
   }
 ]