Revert "docs: add isMissing to boom on types (#294)"

This reverts commit c35a140.

Author: devinivy

lib/index.d.ts

@@ -23,13 +23,6 @@ export class Boom<Data = any> extends Error {
      */
     isServer: boolean;
 
-    /**
-     * if true, indicates that auth is missing credentials and triggers a try on the next
-     * auth strategy. See https://github.com/hapijs/boom/blob/master/API.md#boomunauthorizedmessage-scheme-attributes
-     * 
-     */
-    isMissing?: boolean;
-
     /**
      * The error message
      */