delete clipboard properties after pasting them

https://tronche.com/gui/x/icccm/sec-2.html#s-2.4 specifies:
> Once all the data in the selection has been retrieved,
> the requestor should delete the property in the SelectionNotify request

Most Clipboard-Owners ignore whether or not the property is already set,
so this is mostly a cosmetic change to keep the windows property list clean.

However, at least synergy decides to wait for the requestor to delete
the properties if they are already set by a previous paste (from synergy).

Signed-off-by: Christoph Lohmann <20h@r-36.net>

st.c

@@ -1151,7 +1151,6 @@ selnotify(XEvent *e)
 	 * Deleting the property again tells the selection owner to send the
 	 * next data chunk in the property.
 	 */
-	if (e->type == PropertyNotify)
 	XDeleteProperty(xw.dpy, xw.win, (int)property);
 }