[stdlib] Dictionary.Index: Remove duplicate definition for _isNative

Author: lorentey

stdlib/public/core/Dictionary.swift

@@ -1856,19 +1856,6 @@ extension Dictionary.Index {
   }
 #endif
 
-  @usableFromInline @_transparent
-  internal var _isNative: Bool {
-    switch _variant {
-    case .native:
-      return true
-#if _runtime(_ObjC)
-    case .cocoa:
-      _cocoaPath()
-      return false
-#endif
-    }
-  }
-
   @usableFromInline @_transparent
   internal var _asNative: _HashTable.Index {
     switch _variant {