Fix Type Error on swal

Fixes #890

```
ERROR in node_modules/sweetalert/typings/sweetalert.d.ts(4,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'swal' must be of type 'typeof import("C:/proj/node_modules/sweetalert/typings/sweetalert")', but here has type 'SweetAlert'.
```

Author: doggy8088

src/sweetalert.d.ts

@@ -1,9 +1,4 @@
 import swal, { SweetAlert } from "./core";
 
-declare global {
-  const swal: SweetAlert;
-  const sweetAlert: SweetAlert;
-}
-
 export default swal;
 export as namespace swal;

typings/sweetalert.d.ts

@@ -1,9 +1,4 @@
 import swal, { SweetAlert } from "./core";
 
-declare global {
-  const swal: SweetAlert;
-  const sweetAlert: SweetAlert;
-}
-
 export default swal;
 export as namespace swal;