See also chrome/browser/ui/app_list/arc/arc_app_list_prefs.cc and discard code to rename Legacy Play Store app info entry to new id.

remove also kLegacyPlayStoreAppId from
chrome/browser/ui/app_list/arc/arc_app_utils.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0b72983659c7b1cad0f46cd9322004ca8d993797

commit 0b72983659c7b1cad0f46cd9322004ca8d993797
Author: khmel@google.com <khmel@google.com>
Date: Wed May 16 19:39:47 2018

arc: Cleanup legacy Play Store app id.

We switched to new unified (Android Play Store and ARC++ OptIn UI) Play
Store id year ago. Now it is time to clean up conversion code.

Test: Manually, no problem observed. Positions are preserved.
Bug:  722675 
Change-Id: Ief70ea26b6ec1b446c72fed63ffec8edf56bb956
Reviewed-on: https://chromium-review.googlesource.com/1062218
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yury Khmel <khmel@google.com>
Cr-Commit-Position: refs/heads/master@{#559232}
[modify] https://crrev.com/0b72983659c7b1cad0f46cd9322004ca8d993797/chrome/browser/ui/app_list/app_list_syncable_service.cc
[modify] https://crrev.com/0b72983659c7b1cad0f46cd9322004ca8d993797/chrome/browser/ui/app_list/app_list_syncable_service.h
[modify] https://crrev.com/0b72983659c7b1cad0f46cd9322004ca8d993797/chrome/browser/ui/app_list/arc/arc_app_list_prefs.cc
[modify] https://crrev.com/0b72983659c7b1cad0f46cd9322004ca8d993797/chrome/browser/ui/app_list/arc/arc_app_utils.cc
[modify] https://crrev.com/0b72983659c7b1cad0f46cd9322004ca8d993797/chrome/browser/ui/app_list/arc/arc_app_utils.h