Remove webstore code for signin that is no longer used.

chrome/common/extensions/api/webstore_private.json

Index: chrome/common/extensions/api/webstore_private.json
diff --git a/chrome/common/extensions/api/webstore_private.json b/chrome/common/extensions/api/webstore_private.json
index 236a065ed5562ef0b006b482ab762c051279d777..6ae32a9d30eb55e3c5d7388a30bdea6a283114b7 100644
--- a/chrome/common/extensions/api/webstore_private.json
+++ b/chrome/common/extensions/api/webstore_private.json
@@ -129,7 +129,7 @@
               {
                 "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'."
               }
             ]
           }
@@ -259,24 +259,6 @@
         ]
       },
       {
-        "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": [