Revert of Enable RL by default

ios/chrome/browser/about_flags.mm

Index: ios/chrome/browser/about_flags.mm
diff --git a/ios/chrome/browser/about_flags.mm b/ios/chrome/browser/about_flags.mm
index 493734add2c76515ccad67973f5cc07d727ea797..eb01c74ff6b4711f5e7c3587d9fbbfd35a2063bd 100644
--- a/ios/chrome/browser/about_flags.mm
+++ b/ios/chrome/browser/about_flags.mm
@@ -234,6 +234,13 @@
     command_line->AppendSwitch(switches::kDisablePaymentRequest);
   }
 
+  // Populate command line flags from Reading List.
+  if ([defaults boolForKey:@"EnableReadingList"]) {
+    command_line->AppendSwitch(reading_list::switches::kEnableReadingList);
+  } else {
+    command_line->AppendSwitch(reading_list::switches::kDisableReadingList);
+  }
+
   // Populate command line flag for Spotlight Actions.
   if ([defaults boolForKey:@"DisableSpotlightActions"]) {
     command_line->AppendSwitch(switches::kDisableSpotlightActions);