Fixed completion for extension function after removing members for implicit receiver from scope.

idea/idea-completion/testData/basic/common/smartCast/MemberExtensionAfterThisSmartCast.kt

@@ -0,0 +1,12 @@
+class A {
+    fun String.foo() {}
+}
+
+fun Any.test() { // see KT-8865 Member extension after this smart cast not working
+    if (this is A) {
+        "".<caret>
+    }
+}
+
+
+// EXIST: foo