Move compiler scripting tests to scripting plugin, remove unused funs

also remove some tests that are covered in the scripting-compiler
tests now.
Part of the cleanup to rewrite scripting to the new infrastructure.

plugins/scripting/scripting-compiler/testData/compiler/use_compiler_internals.kts

@@ -0,0 +1,14 @@
+fun checkInaccessible(name: String) {
+    try {
+        Class.forName(name)
+        throw AssertionError("Class should not be accessible from script via the class loader: $name")
+    }
+    catch (e: ClassNotFoundException) {
+        // OK
+    }
+}
+
+checkInaccessible("org.jetbrains.kotlin.config.KotlinCompilerVersion")
+checkInaccessible("org.jetbrains.kotlin.cli.jvm.K2JVMCompiler")
+checkInaccessible("org.jetbrains.kotlin.preloading.Preloader")
+print("OK")