Don't generate backing field for erased inline class

compiler/testData/codegen/bytecodeListing/inlineClasses/shapeOfInlineClassWithPrimitive.kt

@@ -0,0 +1,7 @@
+// !LANGUAGE: +InlineClasses
+
+inline class Foo(val l: Long) {
+    fun empty() {}
+    fun param(x: Double) {}
+    fun Any.extension(y: String) {}
+}