Fabric: Removing MainQueueExecutor

Summary: We don't need it anymore because we don't use folly::Future.

Reviewed By: JoshuaGross

Differential Revision: D15344961

fbshipit-source-id: a368e600d69e6879f6a98b4a997de85c71186e92

Author: shergin

React/Fabric/Mounting/ComponentViews/Image/RCTImageComponentView.mm

@@ -15,7 +15,6 @@
 #import <react/imagemanager/ImageRequest.h>
 #import <react/imagemanager/RCTImagePrimitivesConversions.h>
 
-#import "MainQueueExecutor.h"
 #import "RCTConversions.h"
 
 @implementation RCTImageComponentView {

React/Fabric/Mounting/ComponentViews/Slider/RCTSliderComponentView.mm

@@ -13,8 +13,6 @@
 #import <react/components/slider/SliderComponentDescriptor.h>
 #import <react/components/slider/SliderLocalData.h>
 
-#import "MainQueueExecutor.h"
-
 using namespace facebook::react;
 
 @implementation RCTSliderComponentView {