[Woo POS] PointOfSaleDashboardViewModel not deinitialized after exiting POS

[staskus]

Describe the bug

PointOfSaleDashboardViewModel not deinitialized after exiting POS

To Reproduce Steps to reproduce the behavior:

1. Open POS
2. Exit POS
3. Open POS
4. Exit POS
5. Open memory debugger
6. Notice PointOfSaleDashboardViewModel and related dependencies are not cleared and appear as many times as POS was opened

Expected behavior

POS dependencies should be cleared after closing POS

Isolating the problem (mark completed items with an [x]):

• [ ] I have deactivated other plugins and confirmed this bug occurs when only WooCommerce plugin is active.
• [ ] This bug happens with a default WordPress theme active, or Storefront.
• [ ] I can reproduce this bug consistently using the steps above.

Mobile Environment Please include:

• Device:
• iOS version:
• WooCommerce iOS version:

WordPress Environment

``` Copy and paste the system status report from **WooCommerce > System Status** in WordPress admin. ```

[dangermattic]

Thanks for reporting! 👍