Only call buildBuffer() when needed.

Turns out, `HTTPRequest`'s call is only needed for internet requests.
Files on the local machine will be loaded directly into `bytes`, leaving
`buffer` empty. Calling `buildBuffer()` will then delete the data.

src/lime/_internal/backend/native/NativeHTTPRequest.hx

@@ -571,7 +571,7 @@ class NativeHTTPRequest
 				{
 					if (!instance.promise.isError)
 					{
-						instance.promise.complete(instance.bytes);
+						instance.promise.complete(instance.buildBuffer());
 					}
 				}
 				else if (instance.bytes != null)

src/lime/net/HTTPRequest.hx

@@ -110,10 +110,6 @@ public function load(uri:String = null):Future<T>
 
 		future.onComplete(function(bytes)
 		{
-			#if sys
-			bytes = @:privateAccess __backend.buildBuffer();
-			#end
-			
 			responseData = fromBytes(bytes);
 			promise.complete(responseData);
 		});