[haxe] Remove superfluous OpenFL imports. Close #2917

Author: davidetan

spine-haxe/spine-haxe/spine/SkeletonData.hx

@@ -30,7 +30,6 @@
 package spine;
 
 import haxe.io.Bytes;
-import openfl.utils.Assets;
 import spine.animation.Animation;
 import spine.atlas.TextureAtlas;
 import spine.attachments.AtlasAttachmentLoader;

spine-haxe/spine-haxe/spine/atlas/TextureAtlas.hx

@@ -30,7 +30,6 @@
 package spine.atlas;
 
 import haxe.ds.StringMap;
-import openfl.utils.Assets;
 
 class TextureAtlas {
 	private var pages = new Array<TextureAtlasPage>();