Remove obsolete fragment identifier from IDE manual download link

The Arduino IDE has an auto update capability. A new version is checked for on every startup, and if available the user
is offered an update.

Although this update can usually be done automatically by the IDE, under some conditions this is not possible. For
example:

- The IDE package in use does not support auto update (i.e., Linux ZIP package)
- The file could not be downloaded due to a transient network service outage

In this case, the user is presented with a friendly dialog that explains the situation and links to the "Software" page
on arduino.cc, where the user can manually download and install the new version.

During the pre-release development phase of the project, the download links for Arduino IDE 2.x were on a sub-section of
the "Software" page. For this reason, the linked URL included the fragment identifier `#experimental-software` so that
the page would load scrolled down to the anchor at that section of the page.

With the 2.0.0 release, the Arduino IDE 2.x project has graduated to a production development phase. For this reason,
the download links have been moved to the top of the "Software" page and the now inaccurate `experimental-software`
anchor removed from the page.

The previous link with that fragment is still perfectly functional, but the fragment to a non-existent anchor serves no
purpose and also miscommunicates the project status to users who notice the URL that was loaded. For this reason, it is
hereby removed from the link.

arduino-ide-extension/src/browser/dialogs/ide-updater/ide-updater-dialog.tsx

@@ -20,8 +20,7 @@ import {
 import { LocalStorageService } from '@theia/core/lib/browser';
 import { WindowService } from '@theia/core/lib/browser/window/window-service';
 
-const DOWNLOAD_PAGE_URL =
-  'https://www.arduino.cc/en/software#experimental-software';
+const DOWNLOAD_PAGE_URL = 'https://www.arduino.cc/en/software';
 
 @injectable()
 export class IDEUpdaterDialogWidget extends ReactWidget {