Remove unnecessary headless property

Author: ERSUCC

src/test/Tests.scala

@@ -1,6 +1,7 @@
 package org.nlogo.extensions.samplescala
 
 import java.io.File
+
 import org.nlogo.headless.TestLanguage
 
 object Tests {
@@ -10,6 +11,4 @@ object Tests {
   val testFiles     = testFileNames.map( (f) => (new File(f)).getCanonicalFile )
 }
 
-class Tests extends TestLanguage(Tests.testFiles) {
-  System.setProperty("org.nlogo.preferHeadless", "true")
-}
+class Tests extends TestLanguage(Tests.testFiles)