[Payments] Add an entry for Payment Request to chrome://flags on iOS

ios/chrome/browser/chrome_switches.cc

Index: ios/chrome/browser/chrome_switches.cc
diff --git a/ios/chrome/browser/chrome_switches.cc b/ios/chrome/browser/chrome_switches.cc
index ac7a0dff6afea2558602bd0443506703fdd95b96..63603100f6dcaa8bbff5d6e11663f58e7fe1fedb 100644
--- a/ios/chrome/browser/chrome_switches.cc
+++ b/ios/chrome/browser/chrome_switches.cc
@@ -37,9 +37,6 @@ const char kDisableLRUSnapshotCache[] = "disable-lru-snapshot-cache";
 // Disable auto-reload of error pages if offline.
 const char kDisableOfflineAutoReload[] = "disable-offline-auto-reload";
 
-// Disable the Payment Request API.
-const char kDisablePaymentRequest[] = "disable-payment-request";
-
 // Disables the tab strip auto scroll new tabs.
 const char kDisableTabStripAutoScrollNewTabs[] =
     "disable-tab-strip-autoscroll-new-tabs";
@@ -88,9 +85,6 @@ const char kEnableLRUSnapshotCache[] = "enable-lru-snapshot-cache";
 // Enable auto-reload of error pages if offline.
 const char kEnableOfflineAutoReload[] = "enable-offline-auto-reload";
 
-// Enable the Payment Request API.
-const char kEnablePaymentRequest[] = "enable-payment-request";
-
 // Enables context-sensitive reader mode button in the toolbar.
 const char kEnableReaderModeToolbarIcon[] = "enable-reader-mode-toolbar-icon";