enhance tests (mostly codegen)

* drop dependency on stdlib/alt-headers in the most tests
* assign to myEnvironment at most once in JetLiteFixture
* more tests do not compile runtime

compiler/testData/codegen/super/basicmethodSuperClass.jet

@@ -1,7 +1,7 @@
 import java.util.ArrayList
 
 class N() : ArrayList<Any>() {
-    override fun add(el: Any)  : Boolean {
+    override fun add(el: Any?)  : Boolean {
         if (!super<ArrayList>.add(el)) {
             throw Exception()
         }