Add API wrapper for multiple device deletion API (#583)

src/base-apis.js

@@ -1230,6 +1230,27 @@ MatrixBaseApis.prototype.deleteDevice = function(device_id, auth) {
     );
 };
 
+/**
+ * Delete multiple device
+ *
+ * @param {string[]} devices IDs of the devices to delete
+ * @param {object} auth Optional. Auth data to supply for User-Interactive auth.
+ * @return {module:client.Promise} Resolves: result object
+ * @return {module:http-api.MatrixError} Rejects: with an error response.
+ */
+MatrixBaseApis.prototype.deleteMultipleDevices = function(devices, auth) {
+    const body = {devices};
+
+    if (auth) {
+        body.auth = auth;
+    }
+
+    return this._http.authedRequestWithPrefix(
+        undefined, "POST", "/delete_devices", undefined, body,
+        httpApi.PREFIX_UNSTABLE,
+    );
+};
+
 
 // Push operations
 // ===============