Override/Implement members: don't add 'external' modifier

#KT-33466 Fixed

idea/idea-core/src/org/jetbrains/kotlin/idea/core/generateUtil.kt

@@ -248,6 +248,8 @@ fun <T : KtDeclaration> insertMembersAfter(
                     }
                 }
 
+                it.removeModifier(KtTokens.EXTERNAL_KEYWORD)
+
                 @Suppress("UNCHECKED_CAST")
                 SmartPointerManager.createPointer((body.addAfter(it, afterAnchor) as T).apply { afterAnchor = this })
             }

idea/testData/codeInsight/overrideImplement/overrideExternalFunction.kt

@@ -0,0 +1,7 @@
+open class A {
+    open external fun foo()
+}
+
+class B : A() {
+    <caret>
+}

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

@@ -0,0 +1,9 @@
+open class A {
+    open external fun foo()
+}
+
+class B : A() {
+    override fun foo() {
+        super.foo()
+    }
+}

idea/tests/org/jetbrains/kotlin/idea/codeInsight/OverrideImplementTest.kt

@@ -334,4 +334,8 @@ class OverrideImplementTest : AbstractOverrideImplementTest() {
     fun testEnumClass4() {
         doOverrideFileTest("toString")
     }
+
+    fun testOverrideExternalFunction() {
+        doOverrideFileTest()
+    }
 }