Allow updater to delete files specified as removed in manifest

[derrod]

Description

Adds a new removed_files array to the manifest which allows to specify files to be deleted.

Originally this was supposed to go further based on this discussion, but most of that seemed kinda overkill for what we actually need.

I wasn't able to build the updater originally, simply using the zlib package shipped with obs-deps fixed that, but ideally someone should document how it's actually supposed to work.

Motivation and Context

With the upgrade to Qt6, running the updater would otherwise leave a lot of orphaned Qt5*.dll files in the installation directory.

How Has This Been Tested?

Built updater, ran it with modified manifest that removed the entry for decklink-ouput.dll and added the path to removed_files like so:

...
  "packages": [
    {
      "removed_files": [
        "obs-plugins/64bit/decklink-ouput-ui.dll"
      ],
      "files": [
...

After running the updater the portable OBS install was updated to 27.2, but decklink-ouput.dll was gone, yay!

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.