refactor(DocumentController): remvoe Open endpoint and its client method

EnvelopeGenerator.Web/wwwroot/js/network.js

@@ -30,15 +30,6 @@
             .then(this.wrapBinaryResponse.bind(this))
     }
 
-    /**
-     * Tell the server that document has been seen
-     * @param {any} envelopeKey
-     */
-    async openDocument(envelopeKey) {
-        return this.postRequest(`/api/document/${envelopeKey}`, {})
-            .then(this.wrapJsonResponse.bind(this))
-    }
-
     /**
     * Add CSRF Token to request headers
     * @param {any} options