Partially revert "xwayland: Always free reply from xcb_get_property_reply()"

Partially revert "xwayland: Always free reply from xcb_get_property_reply()"

This reverts commit d3553c721c0fed07f85b70fea418ca65ed974fbb.

weston_wm_write_property() takes the ownership of the reply it gets as
a parameter, and will eventually free it later in writable_callback.

This change introduced a double-free when Xwayland programs triggered a
copy to the clipboard, leading to a Weston crash.

Reviewed-By: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>