firefox-webext-browser: remove bookmark.import/export (#25044)

They aren't used by any browser and break the bookmarks namespace (no
other properties are accessible on completion)

types/firefox-webext-browser/firefox-webext-browser-tests.ts

@@ -12,3 +12,5 @@ browser._manifest.NativeManifest; // $ExpectError
 // browser.runtime
 const port = browser.runtime.connect();
 port.postMessage(); // $ExpectError
+
+browser.bookmarks.getTree();

types/firefox-webext-browser/index.d.ts

@@ -3915,10 +3915,6 @@ declare namespace browser.bookmarks {
         type?: BookmarkTreeNodeType;
     }
 
-    export {_import as import};
-
-    export {_export as export};
-
     /* bookmarks functions */
     /**
      * Retrieves the specified BookmarkTreeNode(s).
@@ -3986,18 +3982,6 @@ declare namespace browser.bookmarks {
     /** Recursively removes a bookmark folder. */
     function removeTree(id: string): Promise<void>;
 
-    /**
-     * Imports bookmarks from an html bookmark file
-     * @deprecated Unsupported on Firefox at this time.
-     */
-    function _import(): Promise<void>;
-
-    /**
-     * Exports bookmarks to an html bookmark file
-     * @deprecated Unsupported on Firefox at this time.
-     */
-    function _export(): Promise<void>;
-
     /* bookmarks events */
     /** Fired when a bookmark or folder is created. */
     const onCreated: WebExtEvent<(id: string, bookmark: BookmarkTreeNode) => void>;