Drop win-ivcam

[GeorgesStavracas]

Description

Drop the win-ivcam plugin.

Motivation and Context

Apparently this was a prototype from Intel that never really properly launched. Remove the plugin.

How Has This Been Tested?

• Open OBS Studio
• Inhale, exhale
• Try to integrate with win-ivcam
• Fail

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

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.
• [ ] 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.

[GeorgesStavracas]

Draft because I have no idea if this is enough to get rid of this plugin. Windows developers, please help.

[derrod]

Same deal as #7372, was marked as "merge for next major release" and then was never merged, so let's do it today and reduce that PR count!

(Even if that means I'll have to rebase some of my updater PRs D:)