[commonizer] Don't commonize "tailrec" and "external" modifiers

expect external and tailrec were prohibited
in previous commit.

^KT-58536

native/commonizer/testData/classifierCommonization/classKindAndModifiers/commonized/common/package_root.kt

@@ -94,3 +94,5 @@ expect class LL1(value: String) {
 expect class LL2(value: String) {
     val value: String
 }
+
+expect class ExternalClass()