Remove Experimental Flag ExternalAppPromptDisabled

ios/chrome/browser/experimental_flags.mm

Index: ios/chrome/browser/experimental_flags.mm
diff --git a/ios/chrome/browser/experimental_flags.mm b/ios/chrome/browser/experimental_flags.mm
index 5d5d5b2da9ec533903b6474d32af5c2eb3641d70..67bc6f56b25924f96a14552c0256a8400bc895dc 100644
--- a/ios/chrome/browser/experimental_flags.mm
+++ b/ios/chrome/browser/experimental_flags.mm
@@ -33,7 +33,6 @@ NSString* const kEnableAlertOnBackgroundUpload =
 NSString* const kEnableNewClearBrowsingDataUI = @"EnableNewClearBrowsingDataUI";
 NSString* const kEnableStartupCrash = @"EnableStartupCrash";
 NSString* const kEnableViewCopyPasswords = @"EnableViewCopyPasswords";
-NSString* const kExternalAppPromptDisabled = @"ExternalAppPromptDisabled";
 NSString* const kFirstRunForceEnabled = @"FirstRunForceEnabled";
 NSString* const kForceResetContextualSearch = @"ForceResetContextualSearch";
 NSString* const kGaiaEnvironment = @"GAIAEnvironment";
@@ -99,11 +98,6 @@ bool IsAutoReloadEnabled() {
                           base::CompareCase::INSENSITIVE_ASCII);
 }
 
-bool IsExternalApplicationPromptEnabled() {
-  return ![[NSUserDefaults standardUserDefaults]
-      boolForKey:kExternalAppPromptDisabled];
-}
-
 bool IsForceResetContextualSearchEnabled() {
   return [[NSUserDefaults standardUserDefaults]
       boolForKey:kForceResetContextualSearch];