Remove Vsync Via Compositor project setting

[hoontee]

Needs testing from users affected by #19783. This most likely doesn't work, but we'll see.

vsync_via_compositor displeases me, so I have removed it.

Compositor syncing is now permanently enabled under the following conditions:

• use_vsync is enabled in project settings
• The editor / game is running in windowed mode, or is switched to windowed mode
• Vsync is forced off in the graphics driver, which I'm assuming was the cause of Heavy stuttering issue in simple 2D game [Windows 10, Nvidia] #19783

The fix for #35038 is still present.

[akien-mga]

Please amend the commit log to make it more explicit, "Fix" is definitely not an appropriate commit log in our codebase... See https://github.com/godotengine/godot/blob/master/CONTRIBUTING.md#format-your-commit-logs-with-readability-in-mind

The PR description itself is good, but the commit log should follow the same standard.