renderer-gst: Deprecate element wrapping

The function causes leaks in the error case and secondly, wrapping an existing
pipeline is not as helpful as I thought it would be.

Signed-off-by: Jens Georg <mail@jensge.org>

https://bugzilla.gnome.org/show_bug.cgi?id=722021
build: Replace non-portable cp -d

Signed-off-by: Jens Georg <mail@jensge.org>

https://bugzilla.gnome.org/show_bug.cgi?id=722527