UWP: Fix uwptools that does not uninstall package

[moko256]

UWP tools does not uninstall UWP app that the tool installed previously.
This commit fixes it and enable to re-run flutter run -d winuwp.

This will solve them:

• [Windows][uwp] Cannot rerun the app flutter#86996
• UWP run/build failed at master branch flutter#82917

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide] and the [C++, Objective-C, Java style guides].
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See [testing the engine] for instructions on
  writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the [CLA].
• All existing and new tests are passing.

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[chinmaygarde]

cc @cbracken. This looks sound but I am completely unfamiliar with the code. Can you please take a look?

[cbracken]

Thanks for the fix! lgtm!