screencastService: Drop always-copy condition

screencastService: Drop always-copy condition

The check for the Pipewire version was originally introduced in
d32c0348 which states:
> Since it is not clear yet when a proper solution will arrive,
> this makes use of `always-copy` as a workaround for now and
> should be reverted once it is no longer needed.

The check for a stable Gstreamer version with the mention proper fix was
introduced in d7b44319 and carried for the 43 cycle.

By the time Gnome 44 will be released all distros should have had enough
time to update their Gstreamer version - or backport the patches, in
case of not ustream-supported versions.

Thus lets drop it now.

Note: `always-copy` is not suitable for dmabuf buffers as it copies via
mmap.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2609>