Unbreak paste after copy
Last commit in !1142 (merged) was a bit overeager dropping those calls. Those on one hand maybe emit set_selection() events (what we don't want), but on the other hand also clear the owner window (that we pretty much want).
Without the latter, the client would think it owns the selection after a copy, breaking paste operations from other clients afterwards.
Still related to mutter#878 (closed).