Remove IDC_BACK_TO_CALLING_APP which is now obsolete

ios/chrome/browser/ui/commands/ios_command_ids.h

 // 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.
 
 #ifndef IOS_CHROME_BROWSER_UI_COMMANDS_IOS_COMMAND_IDS_H_
 #define IOS_CHROME_BROWSER_UI_COMMANDS_IOS_COMMAND_IDS_H_
 
 // This file lists all the command IDs understood by e.g. the browser.
 // It is used by NIB files.
 
@@ skipping 36 matching lines @@
 #define IDC_SHOW_SYNC_SETTINGS                         40914
 #define IDC_OPEN_URL                                   40915
 #define IDC_SETUP_FOR_TESTING                          40916
 #define IDC_SHOW_OTHER_DEVICES                         40917
 #define IDC_CLOSE_ALL_INCOGNITO_TABS                   40918
 #define IDC_SHOW_CONTEXTUAL_SEARCH_SETTINGS            40919
 #define IDC_CLOSE_SETTINGS_AND_OPEN_URL                40920
 #define IDC_REQUEST_DESKTOP_SITE                       40921
 #define IDC_CLEAR_BROWSING_DATA_IOS                    40924
 #define IDC_SHOW_MAIL_COMPOSER                         40926
-#define IDC_BACK_TO_CALLING_APP                        40927
 #define IDC_RESET_ALL_WEBVIEWS                         40928
 #define IDC_SHARE_PAGE                                 40929
 #define IDC_BACK_FORWARD_IN_TAB_HISTORY                40930
 #define IDC_SHOW_GOOGLE_APPS_SETTINGS                  40931
 #define IDC_SHOW_PRIVACY_SETTINGS                      40934
 #define IDC_HIDE_SETTINGS_AND_SHOW_PRIVACY_SETTINGS    40935
 #define IDC_REPORT_AN_ISSUE                            40936
 #define IDC_PRELOAD_VOICE_SEARCH                       40937
 #define IDC_SHOW_BACK_HISTORY                          40938
 #define IDC_SHOW_FORWARD_HISTORY                       40939
 #define IDC_CLOSE_SETTINGS_AND_OPEN_NEW_INCOGNITO_TAB  40942
 #define IDC_SHOW_ACCOUNTS_SETTINGS                     40943
 #define IDC_CLOSE_SETTINGS                             40944
 #define IDC_SHOW_SAVE_PASSWORDS_SETTINGS               40945
 #define IDC_READER_MODE                                40947
 #define IDC_RATE_THIS_APP                              40948
 #define IDC_ADD_READING_LIST                           40949
 #define IDC_SHOW_READING_LIST                          40950
 #define IDC_SHOW_CLEAR_BROWSING_DATA_SETTINGS          40951
 #define IDC_SHOW_SYNC_PASSPHRASE_SETTINGS              40952
 #define IDC_SHOW_QR_SCANNER                            40953
 // clang-format on
 
 #endif  // IOS_CHROME_BROWSER_UI_COMMANDS_IOS_COMMAND_IDS_H_