Retain path structure for loading paths (#845)

* update retain dir structure logic to use emscripten FS APIs

* remove unused import

* replace error message

pyscriptjs/src/utils.ts

@@ -10,10 +10,6 @@ export function removeClasses(element: HTMLElement, classes: string[]) {
     }
 }
 
-export function getLastPath(str: string): string {
-    return str.split('\\').pop().split('/').pop();
-}
-
 export function escape(str: string): string {
     return str.replace(/</g, "&lt;").replace(/>/g, "&gt;")
 }