settings: Drop the dma-buf-screen-sharing experimental feature

It got introduced when many applications didn't handle dmabufs with non-linear modifiers, trying to mmap and read directly from them, giving disappointing results. By now these should be fixed and other compositors/DEs also don't carry around similar restrictions. Thus drop the feature and use dmabufs on every hardware if the app requested that.

This should improve the screen sharing experience especially on AMD systems.

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Note: removing the setting will make all experimental features reset to default for users that have it enabled (will happen for all users anyway when going from 41 stable to 42 stable). In any case it's save to drop it - users will not accidentally activate autoclose-xwayland.

Somewhat related: !1939 (merged) / !2110 (closed)