Override/Implement: Do not insert super-call into extension body

Such super-calls are not are supported yet

 #KT-4311 Fixed

idea/testData/codeInsight/overrideImplement/overrideExtensionFunction.kt

@@ -0,0 +1,9 @@
+open class A {
+    open fun Int.foo(): Int {
+        return 0
+    }
+}
+
+class B: A() {
+    <caret>
+}

idea/testData/codeInsight/overrideImplement/overrideExtensionFunction.kt.after

@@ -0,0 +1,11 @@
+open class A {
+    open fun Int.foo(): Int {
+        return 0
+    }
+}
+
+class B: A() {
+    override fun Int.foo(): Int {
+        <selection><caret>TODO("not implemented") //To change body of created functions use File | Settings | File Templates.</selection>
+    }
+}