JVM_IR: optimize out redundant delegated property receiver fields

Now this:

    class C {
        val x = something
        val y by x::property
    }

is *exactly* the same as this:

    class C {
        val x = something
        val y get() = x.property
    }

(plus a `getY$delegate` method)

compiler/testData/codegen/box/delegatedProperty/delegateToOpenProperty.kt

@@ -0,0 +1,23 @@
+// WITH_RUNTIME
+val String.foo: String
+    get() = this
+
+abstract class A {
+    abstract val x: String
+
+    val y by x::foo
+}
+
+var storage = "OK"
+
+class B : A() {
+    override var x: String
+        get() = storage
+        set(value) { storage = value }
+}
+
+fun box(): String {
+    val b = B()
+    b.x = "fail"
+    return b.y
+}