Remove javaFilesDir parameter of CodegenTestCase.doMultiFileTest

Create TestFile instances for .java sources similarly to .kt sources,
and write them to a temporary directory via writeJavaFiles in each test
where this is needed

compiler/tests/org/jetbrains/kotlin/codegen/AbstractCustomScriptCodegenTest.kt

@@ -45,7 +45,7 @@ abstract class AbstractCustomScriptCodegenTest : CodegenTestCase() {
         loadScriptingPlugin(configuration)
     }
 
-    override fun doMultiFileTest(wholeFile: File, files: MutableList<TestFile>, javaFilesDir: File?) {
+    override fun doMultiFileTest(wholeFile: File, files: MutableList<TestFile>) {
         if (files.size > 1) {
             throw UnsupportedOperationException("Multiple files are not yet supported in this test")
         }