Remove codegen tests with Java, move testData to boxWithJava/

There'll be a single generated test class like
BlackBoxCodegenTestGenerated

compiler/testData/codegen/boxWithJava/enum/simpleJavaInnerEnum.java

@@ -0,0 +1,7 @@
+package test;
+
+public class simpleJavaInnerEnum {
+    public enum MyEnum {
+        A;
+    }
+}