Remove unused setPersistentIsolateData function

shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm

@@ -337,24 +337,4 @@ + (NSString*)defaultBundleIdentifier {
   return @"io.flutter.flutter.app";
 }
 
-#pragma mark - Settings utilities
-
-- (void)setPersistentIsolateData:(NSData*)data {
-  if (data == nil) {
-    return;
-  }
-
-  NSData* persistent_isolate_data = [data copy];
-  fml::NonOwnedMapping::ReleaseProc data_release_proc = [persistent_isolate_data](auto, auto) {
-    [persistent_isolate_data release];
-  };
-  _settings.persistent_isolate_data = std::make_shared<fml::NonOwnedMapping>(
-      static_cast<const uint8_t*>(persistent_isolate_data.bytes),  // bytes
-      persistent_isolate_data.length,                              // byte length
-      data_release_proc                                            // release proc
-  );
-}
-
-#pragma mark - PlatformData utilities
-
 @end

shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h

@@ -36,19 +36,6 @@ flutter::Settings FLTDefaultSettingsForBundle(NSBundle* bundle = nil);
 + (NSString*)domainNetworkPolicy:(NSDictionary*)appTransportSecurity;
 + (bool)allowsArbitraryLoads:(NSDictionary*)appTransportSecurity;
 
-/**
- * The embedder can specify data that the isolate can request synchronously on launch. Engines
- * launched using this configuration can access the persistent isolate data via the
- * `PlatformDispatcher.getPersistentIsolateData` accessor.
- *
- * @param data The persistent isolate data. This data is persistent for the duration of the Flutter
- *             application and is available even after isolate restarts. Because of this lifecycle,
- *             the size of this data must be kept to a minimum and platform channels used for
- *             communication that does not require synchronous embedder to isolate communication
- *             close to isolate launch.
- **/
-- (void)setPersistentIsolateData:(NSData*)data;
-
 @end
 
 NS_ASSUME_NONNULL_END