Remove kArcTransitionMigrationRequired which is unused

BUG=None
TEST=try

Change-Id: Ic3983403036f8e11749c7969dddd027e8e46d820
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2632391Reviewed-by: Pavol Marko <pmarko@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844110}

chromeos/constants/chromeos_switches.cc

@@ -145,13 +145,6 @@ const char kArcStartMode[] = "arc-start-mode";
 // Sets ARC Terms Of Service hostname url for testing.
 const char kArcTosHostForTests[] = "arc-tos-host-for-tests";
 
-// If this flag is present then the device had ARC M available and gets ARC N
-// when updating.
-// TODO(pmarko): Remove this when we assess that it's not necessary anymore:
-// crbug.com/761348.
-const char kArcTransitionMigrationRequired[] =
-    "arc-transition-migration-required";
-
 // If this flag is set, it indicates that this device is a "Cellular First"
 // device. Cellular First devices use cellular telephone data networks as
 // their primary means of connecting to the internet.

chromeos/constants/chromeos_switches.h

@@ -57,8 +57,6 @@ extern const char kArcPlayStoreAutoUpdate[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kArcScale[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kArcStartMode[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kArcTosHostForTests[];
-COMPONENT_EXPORT(CHROMEOS_CONSTANTS)
-extern const char kArcTransitionMigrationRequired[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kCellularFirst[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kChildWallpaperLarge[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kChildWallpaperSmall[];