Refactor Stella plugin

Summary:
1. Replace old FileSelector with the new FileSelector
2. Remove showOpenDialog from FlipperLib

Reviewed By: mweststrate

Differential Revision: D32667103

fbshipit-source-id: be8da034c2695f83b397b6c7d35bc6aee78d66e5

desktop/flipper-plugin/src/plugin/FlipperLib.tsx

@@ -43,17 +43,6 @@ export interface FlipperLib {
   DetailsSidebarImplementation?(
     props: DetailSidebarProps,
   ): React.ReactElement | null;
-  /**
-   * @deprecated
-   * Will be removed in subsequent commits
-   */
-  showOpenDialog?(options: {
-    defaultPath?: string;
-    filter?: {
-      extensions: string[];
-      name: string;
-    };
-  }): Promise<string | undefined>;
   /**
    * @returns
    * Imported file data.